Good point, but I would offer this:
1) the buyer's guide is pretty indicative of what will happen for the rest of the year. If you were a ski manufacturer, why would you skip the buyer's guide?, If you had the ad $ for an up-front spread, why would you save it for later in the year? The mags will tell you that the buyer's guides and resort guides easily see more eyeballs than all of the other issues combined.
2) Many ads are yet to be purchased. How can the mags rig the results if they don't know who's going to buck up the $?
Speaking of ads, it's pretty interesting to see where the manufacturers have put their money. If you compare the first issues of Powder and Skiing, it's pretty clear that the industry is moving toward Powder.
More important, how many ringers make it into the test? Many manufacturers (and this has been talked about in articles in the ski mags) will enter hand built product that is not representative of production skis. That will certainly skew the results. LewBob