Even Fopp is owned by HMV (they bought them out a few years ago) so there really is little option on the High Street. I can only imagine they're still allowed a certain level of independence since the prices didn't seem to be affected by the takeover
.
'That's Entertainment' and CEX are OK for second hand bargains but for brand new DVDs, it's pretty much HMV or nowt (unless you count the Supermarkets).