Great little debate here.
I think that while some can great results with just heavy pulling movements you only need to look at Olympic lifters and their relatively underdeveloped biceps to show that just pulling movements won't lead to optimal results.
If you hold all else equal, then bodybuilders have bigger arms than other athletes. While genetics plays a role, the emphasis on curls has to count for something. At the same time, doing just curls ithout the foundational work of rows and chins obviously isn't going to do the job.
Remember, it's not an either/or situation and combining both leads to the best results. You wouldn't eat just steak without red wine (well, I wouldn't), nor would you have fish without chips. By the same token, using all the tools at your disposal leads to better results than using one exclusively.