$60/month is the same as Sprint's broadband wireless service. For people living in remote locations where this is really the only option other than satellite, it's not so bad of a deal. $99 is a heck of a price for a pretty netbook.
$60/month for "unlimited" mobile broadband (5 GB per month) is just about a universal industry standard. Want to tether a smartphone? Add $60/month. Want to use a usb/express card mobile broadband card? Pay $60/month.
So, instead of buying the netbook for full price and getting a discounted smartphone or mobile broadband "modem", you get the discount on the device and have the capabilities built in.
Personally, I think it is a good marketing strategy to add netbooks to the lineup. Sure, you are stuck with that netbook - but it is one less device to carry around in your pack. With a bit of hacking, I am sure you could make transform the netbook into a mobile broadband router and avoid buying something like the Cradlepoint PHS300.