I don't the design constraint is an issue here. The reason from Ford is, "as it rolls down only up to 60%, people may tend to keep pressing the button and which may result in early wear". I don't believe this reason to be valid. Rightly said by 350Z, its a way to bypass the issue.
And many of you must be aware of the cheap reasons (Child Safety) they even gave for having the windows rolling only 60% down...
My point is, even Toyota Liva; Mahindra Logan and few more fellows have the same constraint, yet Powered the windows. I guess, Ford is reserving this for the next facelift to hold the market.
May be... But can be a perception as well. I have clocked 12K now, and haven't faced any issues with GC yet. At times, I drove at places where there were no roads... with 4 people on board. Right tyre pressure and sedate driving is the key.