That's true. But it's easier to sell people on avoiding mixing batches, and it catches the most common reliability issues. I'd never personally trust my own files to drives from a single manufacturer, though - I've seen too many problems with that.
The problem with SSDs is that they are too reliable and when they fail they fail reliably. The only reason why they fail is usually an intrinsic flaw in the hardware design or firmware which all SSDs of the same model share equally.
