The draw would be integration, just like Microsoft Office or Adobe's Creative Suites/Cloud. Right-click on an encounter in Realm Works and pick "Start" and the encounter map pops up in Lone Wolf's VTT complete with tokens and stats from the various Hero Lab sheets and integrated content packs. No need to do another step of importing the map or tokens to set up the encounter, fog of war is automatically remembered and can be seen back in Realm Works, etc.
People could still use other systems if they wanted, but convenience and combined functionality can trump better features.
Personally I don't need a VTT; at present I'm running a Pathfinder campaign on a table whose tablecloth is a grid (a
Chessex Mondomat - that guy also hosts a Champions campaign) and we're all set for minis. I can see the appeal of an integrated one and I think it's a logical long-term goal for the company, but for now they've probably got their hands full. :)