Well... An easy to download a client, keep a shortcut on the desktop. The user can track the amount of time invested... Achievements. (People love..achievements)... Extending the audience to a wider level. There are plenty other, however the dev said s/he is trying to push for it. So, I wish them luck. :)
"easy to download" ... please take your head out of your...steam client. steam is the most obnoxious client. it abuses your machine in several ways. in linux all games can now exploit system bugs as root. screw steam. everyone hates DRM, unless it is an app store.
Well, shortcuts can be made to web apps too. But yeah, Steam offers a bunch of other things to games like this; the ones you mentioned, but also a way to pay for the game, a community, and (probably most importantly), exposure. App store for games.
steam is like paypal for gamers. which would be good if integration was easy... but no, you are forced to depend on their fullfledged client with all the DRM and abusive tactics.