I agree that it seems unlikely that people would potentially avoid picking up the starters because they didn't want to use them on a team. I think the more likely scenario is that a player would pick up an unwanted starter and dump it in the PC. That said, if you dumped Pikachu early on, it would be hard to get Bulbasaur, so I could see how people could miss out on one of the starters in that case. Also, I guess if someone routinely avoids talking to NPCs, he might miss some of the starters.
Like most people here, though, I got all of the starters. I also used all of them on my team. Having access to all of the starters was a big selling point of Yellow for me, and as the starters were some of my favorite gen I Pokemon, I never considered skipping them/avoiding them/dumping them in my PC immediately.