If you get $60 back in store credit, then you're only actually paying $40 - but you want Microsoft to include more than $40 of stuff. Capitalism doesn't work like that.
Your choice is between:
* A minimal build for $40 - buy what you want from the store yourself
* A "fat" build with loads of added stuff like Skype, Office, codecs etc that you might not want for $100, $0 store credit.
* A minimal build for $100 with $60 store credit
* A "fat" build for $160 with $60 store credit.
If Windows costs $160 instead of $40, then your Windows devices all cost $100 more and suddenly Microsoft are putting off lots of people who don't have loads of money to blow and would prefer a cheaper (e.g. Android) device instead - and besides, why force people to have stuff on their machine that is only going to get in the way? That's entirely contrary to the "slim and fast" image that Microsoft are trying to push with Win8.
It seems to me that the best (and most consumer-friendly) approach is to aggressively push down the cost of the base platform by bundling nothing and let customers spend money in the Windows Store for stuff they might need but which most customers don't need (like Skype, Office, OCR software etc).
Win8 + Windows Store gives you the perfect solution - you get to decide how expensive your initial Win8 setup is by adding extra software (e.g. Skype) from the Windows Store and paying for it after you buy your Win8 licence or device, and unlike any other solution - your device's expense and initial tools are entirely customized to your unique situation! Yay for customer choice!