It sounds like you're trying to convince yourself that lying as a means to the end is OK. Its a pretty weak argument, or rather excuse to not work hard and do things honestly.
The suggestion that what this founder is doing is "spirited optimism" is sickening.
My point is that it's not a good idea to get overly worked up about someone in sales stretching the truth a bit. Sales is the part of the organization that responds to customer needs, and so if they promise a feature to a client, you as the developer are more likely to end up building that feature than if it was never promised and the sale was lost.
It's an imperfect system, but at its core it's not any different from Ford running a commercial that suggests that its operations actually benefit the environment. People believe what they want to believe in order to give themselves an excuse to buy what they want. If the founder in question is outright lying, then he's just not very good at helping customers rationalize the purchase.... :)
The bottom line is that it's tough to bootstrap a company and sometimes the salespeople will "throw the ball ahead of the runner" a bit.
The morality has to do more with whether or not the founder believes that what he's saying will be true soon enough that telling the customer that info isn't misrepresenting the company.
If you went to work for a big company you'd sit in a cube and not hear any sales conversations, but they'd probably be much more distorted -- at least in a startup everyone can help make the dreams (of the founder and the customers) a reality... there is much more of a team mentality.
When you hear the founder say such things you should be thinking "wow, he really believes that we can do that" and feel motivated by it. It's part of the entrepreneurial psychology. He has you on the team b/c he believes you can make whatever he says true.
If you don't like spirited optimism, I hear the IRS is hiring :)