If a company has: a mature HR process, people who know wtf they are doing, and give a crap, they'll do rejection letters. Most lack at least one of those things.
The guy at your SMB example is some jack of all trades, and dealing your resume is a priority-2 in a sea of P1's. He doesn't have a recruiting process. Google does, but even there it's still dependent on a human making a judgement call about what to write.
