On our Contribute! page, Simon reports this reshaping of a slang expression that, according to him, “has become common in England and Wales over the last ten years”. Indeed, he notes that _can’t be asked_ and _can’t be arsed_ sound nearly if not totally the same in some English accents.
A Google search suggests that the idiom _I can’t be arsed [doing/to do…]_ is still essentially British: 69,700 GHits with the spelling _arsed_ vs. only 3,880 that employ the American English equivalent _assed_.
However, an informal survey among a small number of American English speakers hinted at this idiom enjoying a growing popularity in the US while retaining the British English spelling _arsed_, “to express a quaint Englishness”, as one person put it.
That the form _can’t be asked_ is indeed an eggcorn, and not merely the result of deliberately weakening a taboo term, was confirmed to me by Jeannie Cool, who, citing the authority of a friend of hers, expressed the opinion that _can’t be asked_ was the original, “correct” term (and should therefore be the one employed in writing) whereas _arsed_ was what she saw as a slang corruption.
Several of the above examples were selected because they occur on web pages that contain other taboo words a short distance from the quoted passage and are therefore unlikely to have been used in order to avoid writing _arsed_.
_My thanks to the members of the `#suwcharman` and `#wordpress` IRC channels on `freenode` for reports on their usage._
[Update C.W., May 21, 2006: Added Ken Lakritz’s _half-asked_, with cites. The addition makes this something of a hybrid eggcorn. The idiom _can’t be arsed_ is clearly British, whereas _half-assed/arsed_ appears across English varieties. The spelling of the latter doesn’t seem to follow a clear-cut distribution. The Guardian Unlimited site, for example, contains, according to Google, 117 occurrences of _half-arsed_, but also 77 of _half-assed_.]