Package types are not size designations. Pin count & pitch matter more than QFP vs. TQFP, and the dimensions of one manufacturer's TQFP can easily be different from an others, so the datasheet is key.
Yes, for designing a product people must refer to a datasheet.
But when discussing things it's nice when someone can correctly say "TQFP", or when they see a choice of two ICs and you say "It's the QFP one" and they can pass that tube over.
You're correct, but you missed the point. I should have said QFN not QFP, and I should have been more precise. A QFN looks and is superficially very similar to a TQFP. If you look at an example like the PIC18F26J50, you'll notice that it is available in either a 44QFN or a 44TQFP. If you then look at either footprint in a layout editor or gerber viewer you'll notice that they are visually very similar in size and general appearance (and the pinout is almost the same). It is quite easy to confuse the two even by yourself, much more so if you are coordinating the efforts of several people (engineer, CAD operator, purchasing agents, etc.)
