That's assuming that this 51 GB HD-DVD can be played in the currently distributed HD-DVD players. If not, it's not HD-DVD that would win, it would be HD-DVD v. 2.
Also, you can buy dual-layer BR burners right now, for data backup/storage. How long will it be before you can buy a burner capable of burning triple-layer HD-DVD discs?
And how much will it cost to make a triple-layer disc?
And how about BD-J on HD-DVD?
The PS3 is carrying Blu-Ray into many more homes than HD-DVD right now, and will continue to do so in the foreseeable future unless Microsoft integrates HD-DVD into their XBox 360 refresh.
Given the greater studio support for Blu-Ray, the only advantages to HD-DVD are that it's cheap to get into if you've already paid for an XBox 360, and you can watch Universal content on it.
Conversely, it's cheaper to get into Blu-Ray with a $500 PS3, and you can watch Disney and Sony content (Casino Royale, Spiderman 3, etc.) on it.