There's a really interesting presumption in some of the comments on this post. Namely, that getting the job after an interview is the default outcome, and that any other represents an exceptional condition.

In every place that I have worked, making an offer (and landing the candidate) is the exceptional condition. Each step through the recruiting process (resume submission, one or more phone screens, one or more rounds of interviews, extension of an offer, and negotiation around terms and conditions) results in fewer and fewer candidates. I have no idea what the pass rate for each stage is at a typical high-tech company, but I would guess that it could be between 10% and 15% at best.

In other words, odds are that you are not going to get the job.

Separately, there's no reasonable and legally defensible way to provide official feedback if the interview process results in a no-hire decision. The interview is your chance to put your best foot (brain?) forward. If you got post-interview feedback that said "Your linked-list implementation was O(N3) and we wanted O(N)," or "Several of your responses were not in harmony with the way that we like to build systems" how would you respond, and how would hiring companies and managers handle the situation with any degree of efficiency? You had your chance (the interview) to make the case.