Correct. Leg length differences can almost always be accommodated by changes in seat height whereas the getting the top tube length correct for the frame is much more critical.

That being said, there are a number of reasons why people tend toward frames that are too small rather than too large. A smaller bike is usually lighter and has a shorter wheelbase which means that the bike will feel more lively and responsive, which for many people is more important than comfort over the long haul. A bike that is too small can somewhat be made up for by having a long seatpost and/or stem but a bike that is too large doesn't have as many options. This is particularly important for a bike that may be shared for example.