All the comments posted so far are right-- they explain why people might cheer. But nobody has really addressed the very real difference between technology and academic venues (the original poster's question).
I've only been at one academic meeting where people really let loose and cheered. It was in the late 1990s, at a conference on energy efficiency. A presenter brought a pretty fancy bike up on stage and talked about riding it rather than driving. Somebody in the audience shouted out, "Sure, but what did the bike cost?"
There was a moment of pause while everybody recognized the presenter had probably a $3000 bicycle up there. But he hoisted it over his head, stepped back up to the mike, and said, "I'll tell you what it cost... What I was willing to pay!"
The whole audience erupted in a sustained wave of cheers. It was, as other commenters have noted, an expression of approval, an outlet for their passion, and just plain fun.
In some ways, though, I think the setup for that wild cheering was the conflict that it resolved. If his presentation had started out with "This is my bike. It cost a lot, but I was willing to pay it..." I doubt anybody would have cheered. Maybe academic conferences tend to discourage expressions of joy exactly because they tend to formalize conflict, to steer it down certain accepted lines? Whereas tech presentations probably have a lot less inherent conflict that has to be channeled in order to keep it productive?