Demo Fall wasn't the only place startups were pitching to a large group of investors in Silicon Valley on Thursday. More than 500 angels heard investment pitches from a dozen businesses at Keiretsu Forum's expo at Microsoft's Mountain View campus. "I could talk about the growth of Keiretsu and strength of our platform but I think the reason we attracted so many interesting opportunities and so many angels is that it is an excellent time to invest and there is a lot of liquidity in the marketplace,"…