"Almost" can make a big difference when writing stuff where formal style is expected. For instant messaging, yeah, probably one doesn't have to care.

When writing, you put articles before a letter, but they're based on what phoneme they precede. Therefore, when purely classifying letters, there's much more combinations than 26. In hundreds or lower thousands, possibly. Or more.

That's the difference, and for me it's frankly to memorize a big look-up table of most commonly used words (and which articles should precede them), because this doesn't require any effort to me, than to run an "algorithm" translating to phonemes every time I write something. In a quick reading (not reading out aloud, or even mentally mimicking reading something out aloud), wrong article being used won't necessarily get easily picked up. It's the sheer laziness, I guess.