A little over a year ago, James Mirtle (who at the time was the head at From the Rink) tossed out an article promo/blip drawing attention to ESPN the Magazine's The Body Issue. It looked at the increasing size of athletes over the years, and the NHL somehow got tossed in there probably at the last second because they remembered that sometimes Canadians buy their magazine. It's an interesting thought, that NHLers have gotten bigger, and certainly in terms of muscle mass and height there is a difference between the 1980s, for instance, and today. But it might be too easy to suggest that players are solely getting "bigger, faster, stronger" in the NHL. History ahoy...
You'll notice in the actual chart provided by ESPN that NHLers have plateaued in height at 6'1" (1.86m) and (for the most part) weight at around 200 lbs (90.7 kg) since 2000, and I think this gives us an indication of larger things at work. What might be some of the reasons for the plateau?
The fact of the matter is that the NHL's growth spurt was not singularly influenced by a desire for bigger players, or the result of a tougher work regimen. It was actually a confluence of those things in addition to a major shift in the NHL player population. Recall that it wasn't until the 1980s that we were seeing an increase in Scandinavian players, and likewise not for Eastern European (and especially Russian) players until the 1990s. That's important.
Swedish and Finnish men, in general, had been growing steadily over the last 50 years*, to the point now that they are some of the tallest populations on the planet (male average is a hair under 6' or 1.89m). Canadian men grew in size as well, though they have been level at 5'9" (a little over 1.75m) for around a decade, and have not had growth on anywhere near the curve of Swedes and Finns. Americans have roughly had a static average height from the late 1980s onward (though we've certainly gotten heavier). Note that it would be largely American and Canadian players that would be bumped out of the league in favor of Scandinavians or Eastern Europeans.
While bigger on average than their countrymen, NHLers from North America, Scandinavia, and Eastern Europe (not including the Soviet Union/Russia/Russian Federation/whatever you want to call it in this era) followed this growth pattern, such that by the 1970-born cohort they were averaging the 6'1" plateau that wouldn't be reached league-wide until 2000. So a good chunk of the growth could be attributed to older players from a smaller era gradually retiring or leaving the league. But there's also another nifty little slice of the pie in there...
Russians/Soviets comprise a more-interesting part in terms of demographic growth in this period as the country experienced a major regression in height between children born in 1970 and 1975. The average adult height of millions of Soviet citizens born in this period dropped 2-3 centimeters at a time when many European and developing nations were growing 2 centimeters a decade. In general, this was the watershed of a shaky but growing economy without any real "trickle down" and the fallout of drastic social policies; as these were Soviet-centered, they did not immediately affect Soviet satellites (Czechoslovakia and Poland, for instance) demographically. This kind of demographic drop would not right itself quickly, and that makes it very likely that the growth in number of Russian players in the NHL was not necessarily a positive impact on the average size of the league until we had moved a ways past the 1970-1975 cohort. From this cohort, NHL teams had their attention grabbed either by exceptionally-talented, small Russians (of which there were more, such as Valeri and Pavel Bure, Andrei Kovalenko, Vyacheslav Kozlov, or Sergei Berezin), or anomalous big Russians that had been able to knock around smaller players in the Motherland. The former played at a high level, took a beating, and usually stuck around longer; the latter were frequently exposed by the NHL's pace and often found their way back over the ocean (Roman Oksiuta, Alek Stojanov, Denis Tsygurov, and Yan Golubovsky, for instance). You want more names, just take a look at the first 3 rounds of the NHL drafts in the early to mid-1990s, or take a gander at the rosters of the Russian elite teams in the same period.
The end result was that during the first half of the 1990s the 1970-1975 Russian NHL cohort was around 1 to 1.5 inches shorter on average than their North American, Scandinavian, Czech, and Slovakian counterparts. This gap was gradually closed over the following decade.
What I want to call attention to is that we can't lose sight of the fact that the hockey world is not completely separate from the outside world, whether it be demographics, economy, etc. We'd like to think ideological shifts were solely what made players larger, or it was a natural progression, but somewhere in there are players from certain countries that had less food on their plate growing up. We are not bigger than the greater workings of our environments.
* Finnish data was culled from a 2001 article by Silventoinen, Lahelma, Lundberg, & Rakhonen.