Rev-share is the same from what I have seen (desktop v. mobile) but the total revenue per customer acquisition (conversion) is lower in mobile. So the difference in a PPS payout would be reasonable.
I do think there is a big difference between handheld devices and tablets -- especially 10.1 inch tablets. Larger tablets can replace a PC screen in a lot of consumer scenarios and their user's as customer acquisitions are probably comparable to PC customer acquisitions in overall revenues.
Screencasting mobile devices are another consideration but impossible to recognize (I think?)
less than 8 inch = little fish
10 inch to PC = bigger to big fish
^rule of thumb
However, a school of sardines may equal a few large fish in weight
Having micro-payment options with mobile is important -- 'adult' can't participate in that yet easily -- only on closed loop settings -- 1 website, one payment account. A VOD or Clip selling business for example ...