"Apple’s own guidance for the quarter was $25 billion in revenue" - So they didn't miss their own goal.
So the street takes Apple's figures and add 20% because they know Apple always understates by 20%, so on those figures Apple didn't do as well as they should have.
The problem is that you don't know if Apple really expected $30Bn and under-performed or really expected $25Bn and over-performed.
Apple is a public company with shareholders and has a legal(and moral) duty to actually produce honest figures. Ultimately massaging them down is just as bad for investors as talking them up.
If you are deliberately underestimating to be conservative - so if there is an earthquake in Japan you can still make the expectation, or you do it to produce a headline, it's equally bad for your shareholders.
Otherwise why not produce figures saying we might sell nothing next quarter -if an asteroid wipes out all life on earth.
Of course it's still a nice position to be in compared to a company lies about making a profit next quarter hoping for a miracle!
AAPL didn't lie. they're just conservative.
wrong. read my other comment above.