1) WP8 is NOT using more RAM than Android or iOS.
2) iOS Apps are not faster or more efficient than WP8 Apps (despite 'developers' claims above).
3) Microsoft purposely caps available RAM on a 512mb device to 150mb by default, or 180mb if requested by the developer.
4) 180mb of RAM is plenty for games, unless the developer is trying create a game that rivals the Xbox 360. None of these games do or will be anytime soon. (However, if a developer does want to produce a game that looks as good as the PS3/XB360, they can target the 1gb or 2gb WP8 phones, and have enough RAM.)
So why does Microsoft use a hard cap for App RAM usage? Well, the answer comes from metrics used to keep the OS running smoothly without hurting critical background processes. WP8 is reliably fast and fluid, and Microsoft won't let crappy Apps/Games compromise this.
Let's contrast this to Android, and what happens...
On Android if the Game/App is using over 140mb of RAM on a 512mb device, key portions of the OS and critical background Apps will be unloaded from RAM.
This is why you find Android users on lower RAM devices complaining that 'messages' stopped or they didn't receive a notification or missed a call.
When faced with low RAM, Android scrambles to keep what it thinks is important alive, but will cycle off critical processes while doing this, and sometimes is unable to start them again until the Game/App is closed. Android may even terminate an active phone call trying to free RAM for a Game/App that uses too much RAM.
Android also becomes lethargic and slow to respond while running a Game/App that is consuming too much RAM, and slow to recover even after it has been closed.
In contrast...
WP8 is always fluid, no matter what Game/App/Apps the user has open. This is why getting back to the Start screen is instant, and firing up the camera or other Apps while playing Halo is always predictably FAST.
Future Thoughts...
Microsoft may expand the RAM cap for 512mb devices; however, as I mentioned above, unless the developer is trying to shove near 720p graphics, there really is not a good argument for using over the 180mb of RAM limit. (The majority of 512mb devices don't even have high resolution displays.)
Developers do get lazy, and there is also overhead left over in porting to deal with that can later be optimized. This is why you see a 1gb version of the game release first, with a 512mb version a few weeks later. They can get the game out faster on the 1gb devices and then optimize for the OS and DirectX and meet the 180mb RAM limit. (This way no time is lost in getting the game out.)
Again, if 180mb of RAM doesn't seem like a lot, remember that stunning 720p PS3/XB360 games only had around 400mb of RAM to use.
PS - The game that brought this topic up is coming out for 512mb devices, just give them a few weeks.