Android is far more user friendly. The Windows store has never really took off and Windows doesnt really suit tablet mode as much as Android is, for obvious reasons. You have a point about the lack of space though. I dont have a dual boot tablet but about a year ago I considered getting a Chromebook but there was just one .exe program that I simply had to use and bring with me so I got a Windows one instead. Dual boot is for those who just need that one or two .exe on the go. You can I imagine even play the odd old game. The likes of Warcraft 3, Hitman 2 etc. The tablets usually come with USB ports so just plug in a controller and you can play it on a bus to work.
As for size partitions. I think they vary. I did a Google and found this:
http://forum.xda-developers.com/windows-8-rt/general/pipo-w4s-8-dual-boot-64-gb-t3090888
The Pipo w4s had 64gb and 8gb is for Android (4.7gb free). The rest is Windows. There are probably ways to edit partition like the user in the link but you should probably ask before buying a specific tablet.
50gb for Windows is fine. I have a shitty HP Stream and that has 30gb for Windows 8.1 of which only 22gb is usable. Its poor but it does the job. Can play games.
Android really doesnt need that much space.
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