You already can. There is an unlimited play demo for StarCraft 2. So since it doesn't require a subscription, the answer they will give to you about that is "download the demo".

Aye,
But there is a perminent free 10 day trial on WoW - are they telling SC2 users to 'download the trial'? Or are they giving them a months free subscription? Bit of a difference there to my mind. And tbh I think a 'unlimited free DEMO' sort of raises questions as to actually what you can and cant do. If I am to try a game (which I prefer before I buy) then I want the FULL game, not a 'demo' version.

It makes more sense to give someone a set amount of time in a subscription game. And since StarCraft 2 isn't subscription-based, the demo will do.

The demo is limited to a set of stages that make up the first 5 or so of the full game, and multiplayer is available, but limited to Terrans.

If these guys are getting a 30-day version of the trial account, they are getting restrictions, too.

As far as demos go, be glad you are lucky enuf you GET a demo. Most developers say !@#$ off when it comes to demos, and unless you are a console gamer, you don't get one. They don't want people seeing how crappy their games usually are, so they want you to buy it, and make them money. Very few developers offer pc demos anymore.