This isn't my area but I would expect that the quality of the outputs are similair (and in this case digital so .. yes) so the difference if any have to be from the decoder of the video and in this regard atleast for DVDs many of them suffer from "bugs" which makes the output not as good as you would have wanted, so therefor I expect a software based solution to be better if nothing else because it can be updated and fixed.
For the PC I guess a program and CPU will have to do the decoding and if the program is updated all the time and so on I would expect quality to become very good.
On the PS3 I have no idea if decoding is made in some chip or in software running on cell, but probably the later and if nothing else since you can code your own apps for the PS3 I guess someone could make their own player aswell.
So did that help you? Probably not =P, anyway I would have got the PS3 instead of a computer, also probably even instead of a regular blurayplayer since the price is low, it's very silent as it seems and of course because it's a console aswell =P
The 20GB modell just had price cuts and are sold for only equivalent of $320 in Japan, awesome deal for what you get =P