[jameyc]

That's actually correct - 'an' before a sounded 'h' is a style issue in American English, and still commonly used. In nearly every other English dialect it is a strict rule.

[ajhit406]

Yeah I was just going to comment on this too-- "a" vs. "an" actually has to do with pronunciation, not strictly words that begin with vowels.

Maybe the author is Irish =)

[astrodust]

What's peculiar is that "a house" or "a hose" is given to be correct, but "a honour" or "a hour" is not.

It's probably that words with a more French origin, where the "h" is subdued, require "an" where the harder "h" from more Germanic words does not.