That's probably a factor in some cases, to be sure. Wouldn't exposure to strong communication techniques and tools be valuable as well? I've worked with some developers who truly/honestly didn't understand basic email etiquette, let alone useful commenting techniques, version control, etc.

The skills that are defining some of the new breed of web-based companies out there - distributed workforces, able to attract the best people for the job regardless of where they're located - are sorely lacking in most dev shops I've worked in or had first-hand accounts from.

It would also be interesting to me if the 'Sr dev' roles you're referring to had actual time budgeted in to their working day for actual mentoring and guidance of others, instead of just being a 'go to' person for every junior dev's problems, on top of your own workload.