Hi,
A couple of weeks ago my dealer demonstrated the Carvex to me and I had a little go myself in cutting out some circles. The results were amazing. A radius of less than an inch as no problem in the inch and a half material and the cut was dead straight.
The dealer showed me the blade and told me this particular blade is thicker on the cutting edge than on the 'tail' edge. This allows it to move more easily in curves. Looking at the dutch festool site, I find that the S blades have this shape. All the other blades seem to have a straight blade.
This might explain the issue with cutting curves. It is probably not so much the thickness of the blade as it is the shape of the blade.
Mattijs