[_delirium]

It's typically spelled aesthetic in American English nowadays (without the ligature). In that one the NYT was a hold-out in the other direction: esthetic never overtook aesthetic in general American usage, though for a period in the 20th century it looked like it might (encyclopedia did definitively displace encyclopaedia). It looks like the NYT wholesale made the ae->e switch around 1920, and then in the case of aesthetic finally realized it wasn't going to happen, and reverted to common usage in 2000.

[pacaro]

I have no idea how general this is, but in my experience the split appears to be on philosophy (aesthetics) vs beauty salon (esthetician) lines. I've seen the ae spelling used for the latter but not the e spelling for the former.

I love this stuff. One thing I miss about no longer working at Microsoft is the site license for OED

[levosmetalo]

Seems like US English was bussy replacing German umlaut characters ä, ö, ü (transcribed in ascii as ae, oe, ue) with americanized version.

[_delirium]

These words aren't German borrowings, so that isn't related at all. The ae in this class of words is from Latin æ (ultimately from Greek αι). The ae->e shift was an attempt at spelling simplification, to remove some vestigial Latinisms, but only partially succeeded.

[waqf]

Confusingly, though, German does render Latin æ, œ as ä, ö (ästhetisch, ökonomisch)

[_delirium]

True, although I believe than in itself is only a slightly older (circa 1900) spelling reform. In older German books, you see Aesthetik/aesthetische/etc. instead. Lots of borrowing and adaptation...

Ngrams: https://books.google.com/ngrams/graph?content=Aesthetik%2C%C...

Random example: http://books.google.com/books?id=7ZpJAAAAMAAJ&printsec=front...