I agree wholeheartedly. One issue is that every "promise" is a bit unique. HN posters are big on mentoring and interesting work, which are subjective qualifications, but this is not the case for everyone. Some people just want a salary and a chair-- much easier to promise.

The incentive to mentor is long-term. It benefits the company later on, and loyalty is an asset for the person doing the mentoring (his proteges might move with him if he gets sacked). Unfortunately, few people think this far ahead. In the short term, mentoring is an expense.