A big difference between Blu-ray and HD DVD is that they’ve chosen to use two different technologies for their interactive functions. While the HD DVD camp worked together with Microsoft and designed HDi, the Blu-ray gang decided to go with Java. The problem with that is that they still haven’t finalized the specifications for BD JAVA, which has led to that many of the current players will not be able to use future features. The change is expected to come this fall. This includes picture-in-picture, the downloading new subtitles, games, etc. The movies will still work; you will just not be able to do anything else. While a lot of this can be solved through a simple firmware update, there will also be updates of the hardware specifications with minimum demands for the internal storage, something some of the current players fail to comply with.
While HD DVD specified an Ethernet connection as a part of its specification it’s optional with Blu-ray, which unfortunately makes a firmware update even more tedious, if it’s even possible. Not all players support it. Unfortunately there’s no list of the players that are better or worse at complying with the future specification update, but we can only conclude that it has become even more (alas) expensive to stay updated with the latest technology.