That's a valid point. With mechanical stuff we can't upgrade (unless we buy a new one) but then we don't need to - the kit usually works as it should because if it doesn't then it's not fit for purpose and we can get our money back. With software, however, it is rare that it is bug-free like hardware is, so it is generally sold incomplete. It's like buying, say, a food mixer with paddles made out of styrofoam. We assume that these bugs will be fixed (because they can be - it is only software) because if they couldn't then we would return it as faulty.
The other point to note is that firmware updates happen a LOT faster than hardware updates. Why would I buy one this week when I know that next month a newer and far better one will be on the market at the same price (or, as is often the case, cheaper)?