Yes there is a massive difference if you compare both at the same budget.It is possible to get both in one but it costs more.How much depends if you want the latest HD soundtracks from Blu Ray or not.I use a Tag AV32REX192 processor which is a great second hand buy, and a Primare power amp which has 5 monoblocks in one case and it does both really well,but doesn't do HD. if you want HD then the AV amplifier /2 channel gear is by for the cheaper option as HD AV processors are very expensive.
Without a HD processor it is possible to get HD with a Blu Ray with 7 channel analogue outputs, but this requires setting up through the Blu Ray players menu and it starts to get complicated.It also requires a 5.1 or 7.1 analogue input on the processor.
The good news is that a system that does both has a lot less cables!