Do you honestly think they couldn't have found an alternate venue to accommodate demand? If you've been to YC, calling it an impressive venue would be a bit of a joke. It's basically a warehouse (admittedly with an elegantly architected, though extremely spartan, interior). And what does accommodating a few more people have to do with Sam becoming a co-host?
This has little to do with money, and a lot to do with influence (on both sides). Startups are a big thing now, YC is a big thing in startups and Obama/the DNC likely saw value in connecting with this new group of influential people.
Similarly, for Sam/YC, it's an opportunity to move things along on issues that matter.
You stated: "No more money is going to be raised for the DNC than would have happened anyway."
I'm pointing out that the proffered reason they changed venue was to accommodate more people, and thus raise more money. As a matter of fact, no other reason was offered, in particular none of the ones you advance. Unless you have insider knowledge or seen a different announcement?
In DC the message seems to be that the most important thing is who you know. You want to be an insider. In practice this seems to work much as in LA. There's an A List and you want to be on it or close to those who are. The only difference is how the A List is selected. And even that is not that different.
That's simply how Washington works .. influence is their currency.
This has little to do with money, and a lot to do with influence (on both sides). Startups are a big thing now, YC is a big thing in startups and Obama/the DNC likely saw value in connecting with this new group of influential people.
Similarly, for Sam/YC, it's an opportunity to move things along on issues that matter.