As I understand it, the real difference between angels and VCs is that angels invest without locking down a valuation, and angels invest without demanding control. A VC round comes with a firm valuation and with a board seat.
The biggest difference, traditionally, is that angels invest their own money or that of buddies, and that VCs invest the money of LPs. This is a little weirder these days, as there are super-angels/micro-VCs/whatever-their-business-card-says where that starts to become a distinction without a difference.
I think that outside of SV, this distinction is more valid, as the hybrid "we're a VC that wants to look/act like an angel" isn't as prevalent. Probably because the trend towards angels isn't as pervasive outside of SV. But I'm not really up-to-date on the inner workings of raising capital, so I could be wrong.
I mean, if you purchase a percentage of a company at a certain price, you have implicitly "locked down a valuation". Right?