why would it ruin them? Given the valuation people are talking about, they sold less than 15% of the business - they'll probably retain enough control to do whatever they want with it and probably try new things...
I personally know at least one company that has been profitable from the very beginning and took 3 rounds of VC already, always on the same terms: "we don't need your money, so we'll sell you a very small piece for a large sum and run with it the way we do today". In the end, it's a great way to either cash-out, put some money in the bank to avoid future surprises or launch new experiments/products with minimal risk...
is it possible the maximal risk they encountered when building github with their own cash helped make the great product github is today? history has shown time and time again if you give someone a long enough rope they will hang themselves, doesn't mean that's githubs fate of course, but they're certainly opening a door of influence that wasn't around through the initial building of a great product.
I'm not sure there is a correlation between little money and making great products - that's a link people (specially incubators and accelerators) try to force-feed on everyone's throats, but I'm not convinced if having no money produces better/more companies/products than having "too much" money. Anyway, that's all unrelated to the topic here :-)
If you give someone a short enough rope, they'll never be able to get out of the hole...
