If you get an onsite interview or phone interview, they should at least have the decency for a form letter "Thanks for applying, but we chose someone else." (especially after an on-site interview)
I have tried to be courteous to everyone who has applied where I am. However, keep in mind that one recruiter may be dealing with 20-50 applicants in that week.
And it is never fun rejecting people. It is easy to want to put it off.
This is a tragic mistake, because if you are running a company you need to be able to do something much worse -- cut people who are currently working for you.
Unfortunately, we see this more often than not at seed stage companies.