But nobody will pay twice for the same game, one to play at home and one for browser play.
Unless you can input your licence key from the retail copy into this service, it will be quite expensive for "some fun at lunch time".
Plus the infrastructure would have to be huge. If 200 people logged on, the company would need 200 separate high spec PCs to allow everyone in. If 500 people decide to come on, they need 500 PCs. If this take off worldwide, they would need an infrastructure of say 50,000 high spec PCs, so initial outlay would be $50 million just for the PCs

Otherwise if they limit number of PCs available, people will get wuite annoyed having payed, not being able to play.
This is why the simple browser games make more sense, because each server can run multiple users simultaneously.