Hi Kathy
This is not an official answer, but it may help you:
PI has a long cicle timerate. We've being with 1.7 for several months, and I guess that 1.8 would be ready in the next 2 months. So, it may well pass over a year, or a year and a half, untill we'll see the end of the 1.9 era (at least, in active development... It shoul be updated to fix bugs for a long term). I think that it is a pretty reasonable time to not worry about differencial upgrade fees yet. Maybe new users of the 1.9 releases will get a discount.
Of coourse, only Juan's word is the official response, and this is just a guess of his plans. :p