Microsoft had originally planned to release Windows Mobile 7 in 2009. But it then pushed the release to 2010. The cutthroat nature of the smartphone market offers very little leeway for such delays. Besides, WinMo 7 is supposed to be a product that will bring Windows phones up to speed with other contemporary smartphones.
The delay left Microsoft with no choice but to plug Windows 6.5, an interim release, in a manner only accorded to a major release. It is clearly a gambit to prevent WinMo loyalists from abandoning the terribly long road to WinMo 7.