Web based is really a wonderfull solution for many applications but IMHO visual editing in browsers is still not on the level of a desktop app. And if it looks like a desktop application the loaded amount of javascript is a fat client in disguise. For the modeller: just pass a 3 minutes installation.
I followed a training course in Pega Rules Process Commander, and that web modelers had the worst user experience I ever encountered. I simply will not spend my days working with a slow and unresponsive program. Furthermore, I do a lot of work while travelling by train with very limited internet connectivity, which wouldn't be possible with a web modeler.