Earlier quoted context omitted.
I just had a Lexmark tell me cyan, yellow and magenta were low, which was fine since the document I was printing was black text with 2 exceptions for arrows where to sign in red. It printed all the text in orange and the 2 arrows were a perfect red.
There's a setting to tell your printer to not obnoxiously use color inks to print blacks.
However, you don't want to use 100% registration for text as it can easily eat up your ink/toner. A good compromise if you need deeper blacks is 100% K with a bit of CMY (don't know the percentage).
I'm not discarding the idea that printer companies do it so the customer has to buy more ink; that may be somewhat true. However, even high end printers that are designed to last still do this to an extent, so it's not entirely a money grab.