Testers or downloaders?
The "off switch" would only be valuable if the ones who download before the switch is turned would actually use it. By requiring a nominal fee, the downloaders will then be motivated to actually try it instead of just downloading it. I've downloaded the 64-bit version of Windows with my msdn subscription and I don't even have a 64-bit processor on my desktop. I guarantee if I had to pay $1.50 I wouldn't have done that, and MS would have had better use of their resources.