It's not mandatory there as far as I know, so a lot of times it's not available. Besides, why can't they offer FLAC as well? Typical Apple NIH if you ask me.
Can you provide a link to an iTunes Music Store release that is available in ALAC format? I am not aware of any.
You're right, the iTunes Store does not sell in ALAC format. They sell a "Mastered for iTunes" format though, which is encoding the 256Kbps AAC file from a high quality source.
which is not lossless and is completely irrelavent
I'm aware, just explaining what the original commenter might've been referring to.