It may be there to download, but it wont work for some reason.

That's odd, I got both of the PGR4 dlc again though my purchase history after it's been pulled from the marketplace. I suspect that it's probably only a temporary problem, MS should have it available soon.

Games get pulled and put up again plenty of times. Possible they add the GOTY edition soon on it?

My guess is that someone goofed. 

1.  If you buy a game, it will always be available to be downloaded via Xbox LIVE.  Microsoft has stated that time and again.  You may not be able to buy it if the rights to distribute terminate, but for existing licensees the service will maintain a copy of the game for download.  Likewise for DLC.

2.  Microsoft owns Lionhead and published the game.  It would be REALLY hard for them to have a dispute with the publisher or the developer that would require them to stop publishing the game via Xbox LIVE.

My guess is a backend database that houses the game content is offline OR some of the data has been corrupted.  The pointer (link) on Xbox LIVE Arcade is still there, the problem is it doesn't result in a downloaded game.

It is relevant in that people who have bought it cant redownload it.  If you buy a game on disc, you can always put in into another system if it breaks.  However, this seen as one of the limits of digital purchases as a service provider can always delist a game.  For those that bought this game digitally, it is very big news.

I got Fable 2 few years back when they had some glitch on the Xbox.com site and you could add it to the cart for free. Played like an hour...seems like a fun game but not my cup of tea.

VG247

Fable 2 has returned to Xbox Live’s Games on Demand after an “isolated issue” caused the game to become unavailable through the service.

According to a Microsoft representative speaking with Gamespot, the issue has been “resolved and the game is once again available.”

Yesterday, Gamespot reported the news of the game being seemingly pulled through various news tips from gamers.

The title remained in users’ download history, but any any attempt to re-download the Lionhead game was met with failure.

Thankfully, all is fixed now.