One cannot rule them all
It would be a risk to have one edition for all. The first and most important thing that comes to mind is cost. If you look at the editions of Windows 7 and the price for each edition then this will certainly put the cost of the tablets up high. For example when you look at netbooks the price is so cheep partly because of the fact Windows Starter is generally included.
Another reason is that having all those features available whether installed or not will take up considerable amount of space, which in a tablet is more valuable considering many tablets have from 16GB up to a maximum capacity of 64 GB. And with Windows 7 (as an example spec.) requiring between 16 and 20 GB depending on whether you use 32 bit or 64 bit editions it would mean that a typical tablet would require 32 GB to be of any use. And that comes back again to the price of having that much required space available.
In summary, keeping the price of tablets down will be key to its success. Maybe its possible the Store icon will be a portal to allow additional features from the advanced editions to included.
