I just wanted to jump in really quick with three quick points.
First, virtual table tops are definitely not MMORPGs!
Second, I have been using one,
Fantasy Grounds, for a long time now. I have really enjoyed the experience. Those interested in flexibility might look into the rulesets that are already available for Arcana Evolved and Iron Heroes for Fantasy Grounds. More will certainly come with time. Whether WotC ever produces rulesets, we will have to wait and see. The great thing is, you do not need them to play. You can play with the books, just like face to face using Fantasy Grounds.
Third, there is an upcoming virtual convention to showcase a number of these applications, including Fantasy Grounds. Check it out!
Part of what they have done is prepared a fairly comprehensive comparison chart between any of the developers that replied to their inquiries.
This is a direct link to the chart. So, you need not rely on my opinion, you can compare them. (Using the chart, or the demos that are available.)
*Disclaimer: I am not employed by either the developers of Fantasy Grounds or the coordinators of iCon. I am just a forum member and satisfied user of Fantasy Grounds.*
Later.