yes, an old-fashioned browser plugin wouldn't make much sense. it would be a lot of work to maintain, making it secure would be very hard, most people won't be eager to install it,...

but there are other solutions coming up like google's native client. it doesn't have the issues of a plugin.

i think being able to play games directly in the browser without the need for installing anything would be a huge advantage and open up a lot of business possibilities.