I think the worry is about the other direction. Want to offer something to people who only pay for this limited access? Then you better don't do anything these sites don't like, because you have to use them to communicate with your customers (unless you are already big and powerful enough to negotiate such deals yourself)

But people won't know there is "full" Internet access, or will be unable to justify the cost versus making do with the "free 38".

At present in the UK my monthly broadband connection costs just over one day of minimum-wage salary. Or nearly a week of groceries. I can see how easily that could be seen as a worthwhile saving for people on low incomes.