Hi
Where I work we always make the effort to respond, whether positive or negative, just because we believe it's polite to do so, but having said that we don't run a business which is likely to have appl;ications in the 10's or above. I do know though, from HR discussions with other agencies, that is mostly common practive now not to reply, either because they have too many applicants, not enough resources, or just can't be bothered to do so. I can sort if understand from am employers point of view if there are a lot of applications for one post. I work for a charity and we are getting the same with fundraising buds - we just never hear back! not great when people's jobs are on the line!
It would helpful though if they could state on the advert or application pack, if you don't hear by x date, then you have been unsuccessful.
You can ask for feedback from a job you have applied for, if you think it may help.