The most common vowel sound in English isn't A, E, I, O, U or even Y. It's the schwa, and it sounds more like "uh."
The schwa is written as an upside-down "e," and you hear it at the end of "sofa" and in the middle of "memory."
Amazingly, it can be spelled with *any* vowel letter. The A in "about"? Schwa. The O in "gallon"? Schwa. The E in "taken"? Also schwa.
The schwa is also one reason English spelling is so unpredictable — because so many different letters can represent a single sound.