it must be agreed with, at least in some instances; companies can be very rude.
although in a sense they are the ones providing us with a job (which they don't have to do), the human resourcing departments can be quite unresponsive/non-existant. i'm sure these places have a lot of people applying for probably a few jobs. but where there are many applicants, there should be the right staff and departmental structures to deal with such numbers, respectfully. printing off cv's and filling out countless application forms can be very boring and time consuming, and i think that it's nice (even if you receive a letter of rejection) to get some feedback and concern.
with regards to selfridges, i must have applied 2-3 times through both selfridges and an agency this summer. i called up selfridges after hearing nothing from a human being (just an automated email saying they'd received my online application), and they said that if not hearing anything after 21 days it means that you're usually unsuccessful. but she said you can apply again just for a different section - i.e. foodhall instead of menswear. so i'm presuming it might not be a bad idea just to apply to every available position within reason. another thing, is that it's a bit of a silly way to apply for temporary work over the summer via the internet. i usually find it better to talk to someone in person, or at least on the phone, and tell them you're after a month or two's temporary work over the summer. when filtering online applications, they probaby (in my opinion) immediately chuck out those who can't commit for at least 6 months.