Angel funding is often very different than VC funding.
Considering that tweetdeck appears to have been the work of a single person so far, angel funding could make a lot of sense. $500,000 should carry them a long way without all the "overhead" that typically comes with VC funding.
He could have seen many things, but most likely saw 1 highly productive dude that could likely crank out a $3-4MM "company" on a shoe string.
Angel investors/groups are often individuals who want to contribute mentoring as much as money. In many cases, it's like a hobby to them, a way to stay engaged in a business/market without really having to get into the full headache of running/starting a company.
if twitter is an new protocol, the portals to that protocol are valuable. I have 10 columns open in TweetDeck to monitor things I care about on twitter. There will most certainly be opportunity for premium services, and other creative ways of making money.
