Been out of the loop for a while and happened to pop in. Bottom line on this firmware thing is that the only difference is the GUI between the two. The menu graphics are the only differences and granted, the new menus and such are nice. No doubt that the GUI changes has been in the works for a while now. Don't be surprised if the exact same interface comes to the XG in the not too distant future. By releasing it to the XH first, they get to hear feedback from a smaller group (much easier to respond to if the response is negative). Once they are happy with the consumer response to the interface then they can feel more confident with a much larger release to the other models that can/do support it.
As far as all the comments about crippling firmware...that's a bit disingenuous. Every single manufacturer controls "their" firmware to establish their product line. Thanks to the discount of scale, it ends up being cheaper for them to buy hardware that has the capability of supporting their desired features for their flagship product. They can then "dumb-down" said hardware via firmware to establish their product line. If you want all the bells and whistles you pay for the flagship...if you don't care about those things you save money and move down the product line. That's the way things work, have worked, and will continue to work in the CE (and most other) world.
Just my $0.02 worth...I'm sure I'll get flamed but who cares.
Man cave: Sony XBR75Z9D, Marantz SR8012, and OPPO UDP-203
Living room: Sony XBR75X950G, Denon x4500, and Sony UBP-X800M2