At that Blizzcon, there were multiple areas with stage sets, most notably Diablo and it's rooms of oddities, altar for sacrificing the innocent...I really don't recall if there was one for SL; I played the demo for D4 and SL but I don't recall a themed SL area. The Hearthstone area had a full set and the trading area had...something...it's been 4 years and I'm old, I think I've just forgotten what the WoW area looked like.
Standards? Not really. There are 2 basic types; what some call 4x4, where two sides are formed into the rectangles you see, and the sides are closed but with cutout for the forks of a lift truck to slide into; these are 48" x 40", and you can fit 26 in a trailer if you orient them in a specific way. The other types have the rectangular opening on all sides, which are easier to maneuver then the ones with the cutouts, but they tend to break if you don't lift them correctly. Most companies will use recycled ones because they are cheaper than buying new, but a company like Blizzard might see that extra cost as negligible so maybe they only use new ones. I've worked in logistics for 12 years and most companies, even huge brand names, use whatever is cheapest.
Speaking on logistics, when it comes to conventions/trade shows, the schedules are generally tight. For big shows like CES, the work starts a month before due to the scope of the show, and while Blizzcon is really big, they seem to be working on a tighter schedule, so it is not surprising that the sets are coming up already. My guess is general construction will be done Thursday morning, allowing the QA team a walk through with the production company. I assume Blizzard works with one of the large outfits like Freeman or GES, but I don't know for certain.
I actually tried to get Blizzcon to Vegas, offering our warehouse as a hub for storage and delivery, but was given a polite no.