Each time I use my tablet I wonder if anyone considered deeply usage of bottom bars.
Let's take Xournal for example.
On PC - it has top placed menu bar, on tablet - bottom.
Why? Just because someone build tablet's browsers that way?
Of course it's more comfortable to work with stylus on the bottom area of the screen but - hey - in fact no one types in browser addres window directly - the keyboard shows up and we "type" - at the bottom of course.
From my point of view the bottom screen's area is too precious to put some fixed bars here - just like almost any app does.
On the other hand - hildon desktop seems free from this issue since it has it's bar on the top.
This is the way we could avoid some silly behaviour when in full-screen mode right scrollbar flickers at the bottom because additional webpage elements are being downloaded.
To sum up - don't You think that top placed bars in applications (especially in fullscreen) are more comfortable than bottom ones?