I've never tried to get the samples from microchip before, never really had a reason to. They're just so inexpensive to add on to an order, and I order parts and just fairly often, I just toss a few on. Plus as was just mentioned, you can get them really cheap from Glitchbuster.
But I look at it like this: If they're willing to give free samples to select people, then those people shouldn't feel guilty taking them. There are Chinese food places in the mall that I walk by. I already know I like the food, and sometimes stop and order a meal. But anytime I walk by and they have a person out in the walkway giving away free samples, I always take one, regardless of if I feel it's going to generate them a sell that day. I realize this analogy fails as MChip is being selective about their recipients. But if they're willing to give samples away, and you aren't on a non-distrution hit list, then I see no problem.
Only giving to corporate entities (many of who have hojillion dollar contracts) who could -easily- spare $20 for a few chips to demo seems silly, especially considering other manufacturers whose initial development kits cost hundreds. These samples should be for anyone who has a need to use them. When you go to sell stuff on ebay, there are additional restrictions for people who use hotmail and yahoo addresses. This is similar. They don't want to just give them to random people off the street. They want their target audience to have some kind of legitimacy. "Here, check out our 16F628 and see if it meets your needs. Yes? Awesome. Now order some next time."