At the people calling the Marquee a tent, consider the following.
It cost about ?150 to hire the Big Bash hall for about 10 hours. Those Marquees cost about ?15K. Ok so that particular marquee didn't have a wooden floor but I bet it still cost a shedload.
I think Kudos are in order for the organisers.
And what event could be better for launch than the home of British computing ?