Well, there is a difference between endurance and strength.
In weight lifting, one can think of strength as the maximum amount of weight you can lift for one rep. Now working out to maximize strength is very different then working out to maximize endurance.
I did some weight training a number of years back. I was told it would help my cycling. It didn't. Maybe for some people but not for me. I did go out and ride with some of the top body builders in the gym and they were competitive at the national level and pretty strong. But they couldn't hit a high enough rpm to go faster then 24 mph in the big gear so dropping them was easy. Just get them up to 24 mph and put on a burst.
I also noticed that none of the weight lifting exercises did anything for my cardiovascular system. Most people sat around awhile to catch their breath after a set. I would just move on and work another muscle group because the weight lifting rarely got my heart beating elevated much. I was pretty much working on upper body and those muscles just were not big enough to tax my cardiovascular system.
I was impressed that the body builders did have reasonably good cardiovascular conditioning, but not like me, a cyclist.
The thing is that cycling involves very high rpm work for long periods of time and it involves much more cadiovascular training then you will find in most gyms unless you get on a stair climber and go nuts.
Now don't get me wrong, I am not denigrating weight training. Doing a balanced weight training routine several times per week is a great idea. It will make sure that all of your major muscle groups are in reasonable shape and reaonably strong. So if you go out and decide to do something out of the ordinary physically, you will probably be able to do it without killing yourself.
But for training for cycling nothing beats getting on your bike and riding.