This shouldn’t be a total shock but Microsoft is going all in with Windows Phone, so the fact that the Windows Mobile Marketplace (NOT Windows Phone Marketplace) is finally being put out to pasture. The Windows Mobile Marketplace never really did that well and peaked around 7,000 applications. Applications in that marketplace were also too expensive when compared to the Apple App Store in regards to competition.
The Marketplace launched back at the end of 2009 but didn’t have that much time to breath before having the plug pulled at the hands of the Windows Phone Marketplace at MWC in 2010. The shafting of the Win Mo Marketplace was something that needed to happen eventually and will allow them to refocus resources in to making Windows Phone better.
All apps you have on your Windows Mobile 6.X device (assuming you actually still have one, hehe) will continue to function but you wont be able to re-download them obviously. Besides I’m sure that XDA has been the life support in regards to Windows Mobile development anyways. Hit them up!
Or, you know, you could get a Windows Phone with 60,000 and counting apps :p