Yes, it can be used both ways. I saw an advantage in this aswell, but a different one: if you're using a 3m long guiderail in a confined space, you don't need to monkey around, or even go outside to turn it around. ( I have come across this situation often enough, I have even seen that at least one person here has 2 3m rails in his shop for this reason).
The dewalt plunge saw has 2 grooves in it's base, the middle one is for it's own guides, the off-centre one is compatible with the festool rails. If festool would make a similar rail for it's saws, it would have to be much wider and not practical (or redesign the base).
The downside of the rail with rubber strips on both sides is that you can't use the rails conveniently for marking or cutting with a utilityknife.