there are two HD dvd formats. Blue Ray is owned and marketed by sony, hence its inclusion within the play station 3.
HD is the other format.
The xbox 360 add on hd dvd player used this second format and in all respects is a standard HD dvd player.
However, and i say this as a huge 360 fan, there has been some criticism that the 360 HD dvd player can be a bit jumpy especially during fast action sequences. This is apparently more noticeable on a larger screen but I haven't seen this myself only have other work for it.