Okay, let's make a couple of assumptions here.
Seinfeld tells Gates they need to connect with "ordinary people", yet fail to do so miserably to the point where they are kicked out the house. The ad makes fun of both Gates/Seinfeld and the somewhat crazy family they are staying with. The fact that Seinfeld is in the ad means that it's supposed to be funny, regardless whether or not it appeals to the viewer.
So they're trying to make a funny ad that is memorable and builds brand awareness perhaps. So why make Gates & Seinfeld look like a pair of rich, out-of-touch jerks? Maybe because that's the stereotype people have of Microsoft.
I think idea here is that Microsoft is showing humility and showing that they are trying to change. They need to make fun of themselves first before they can begin telling people how great they are. That's why the ads have been kinda humble and low-key, rather than screaming: "GO BUY WINDOWS BECAUSE IT ROCKS!!"
I agree with melgross that the ad is a failure if you have to try and figure out the hidden meaning behind everything, so I'm guessing that was not the point of the ad. That's not to say there aren't any hidden messages - just that they're not supposed to be important.
The real message is far more simple, and it comes right at the end of the ad: regardless of how awful, or out of touch Microsoft are, their product (Windows) helps connect billions of people every day.
Or to paraphrase: "Yeah, we know you all hate us now, but you have to admit, we are kinda awesome..."
At least that's the impression I get from seeing this ad. Not that I agree with their message