Quite funny discussion in here.
The thing about studies is that they all show different results. A couple of years ago we were adviced only to eat 3-4 eggs a week due to cholestorol(at least here in Denmark), and a couple of months ago a new study showed that there were no significant increase in cholestorol by eating more than 3-4 eggs a week. One day broccoli is the best thing you can eat, the next day a study has shown that it can lead to cancer. Etc. etc. Several members here have the idea that weighttraining does not affect bikeperformance, others have the idea that it does. Some studies show that it does, some that it doesn't. So what to believe?
My overall belief is that if you combine the two in the off-season, then you should be able to see good results. What makes your legs stronger? Doing squats or cycling? Well since most weightlifters are doing squats, maybe the answer lies here, but that doesn't mean that you will be able to cycle faster, longer or harder. My initial thought is that increasing my leg strength by doing squats, 1 legged leg press and calf raises with low repetition and heavy weight, will benefit me when riding. It has been my experience earlier that this has helped a great deal, but at the same time I have increased my cycling volume, so whether or not the weight training bears the total benefit here I don't really now.
One thing you can never underestimate is the placebo effect of training. If you feel your legs are stronger, and you can feel every muscle working in your quads, then you might get an extra boost.
Like Tapeworm suggests, there are many reasons to do strength training. It may enhance your performance on the bike, just don't count on it. For me it has worked to some extent, and I really like to say that I can squat 125 kgs
If I remember correctly, Chris Anker Sørensen of Team Saxobank did strength training last year according to his blog.