I am the other Sachin Agarwal (at Dawdle.com), and I know nothing, but I will say this: I will bet you a beer that you're wrong.
As an acquiror, you want to do a deal as cheaply as possible. Given that Slinkset never really took off while Posterous has, a deal was probably done in the sub-six figures or perhaps none with just offers of employment. At this point, even though you lose the cash, it's cheaper to use $50K cash than $50K in stock given that you'd reasonably expect the stock to appreciate in value at this point. Acquisitions usually only happen in stock in either "pooling" transactions (i.e. Kayak/SideStep), where the acquiror cannot afford to pay cash (i.e. pick your keiretsu deal from the late 90s), or the seller values the stock more than cash (i.e. Twitter/Summize).
Why, yes, I am a former technology M&A investment banker.
It depends on how much you want them versus how much they want you. If you can't attract them with just cash, you're going to have to give stock. Considering the Slinkset guys are hungry entrepreneurs who'd probably want a stake, and an all-cash transaction in 6 figures wouldn't make them f@#$-you rich anyway, I'd guess this was a most- if not all-stock deal.
It also depends on what Posterous's cash situation is like; if much of the 750k is lying around idle, they'd want to spend it, else they'd rather avoid having to raise money again, which would result in giving up even more equity. Plus, all else being equal, I'd rather share equity with cofounders/employees than with investors.
I also know nothing of the deal, but think your frame of reference is off.
At this scale and early stage -- both companies appear to be pre-any-revenue -- both teams should be most interested in the promise of long-term equity appreciation. Posterous isn't rolling in cash, and rather than shuffling around any cash balances either company has, all cash should be going to a longer runway. A pure stock-and-job-offers deal seems most likely.
As an acquiror, you want to do a deal as cheaply as possible. Given that Slinkset never really took off while Posterous has, a deal was probably done in the sub-six figures or perhaps none with just offers of employment. At this point, even though you lose the cash, it's cheaper to use $50K cash than $50K in stock given that you'd reasonably expect the stock to appreciate in value at this point. Acquisitions usually only happen in stock in either "pooling" transactions (i.e. Kayak/SideStep), where the acquiror cannot afford to pay cash (i.e. pick your keiretsu deal from the late 90s), or the seller values the stock more than cash (i.e. Twitter/Summize).
Why, yes, I am a former technology M&A investment banker.