I think the people doing the 2-year-hop are the ones with a lot of inbound interest. The last two jobs I've had (including my current job) came to me through a direct inquiry from someone at the company (not a recruiter / headhunter). The thing with consistent inbound interest is that it creates zero incentive for putting up with non-regular advancement / promotion (except the 'devil you don't know' risk, but that can be ameliorated by asking around. It's not hard to avoid a completely blind scenario) because the perception of "job hopping" becomes irrelevant. I suppose at some point the inbound interest might taper off but until it does, it's almost irresponsible to ignore better offers.