I actually mentioned this in another thread the other day - there is no P-38 of any sort in MAW; Greg has given the reason above. Dancat's P-38F is the right one to have for Op. TORCH, as far as I know. (US aircraft that were not used by the RAF remain a closed book to me...) The Lightning was rejected as a fighter for pretty obvious reasons - it could survive against Me109s and FW190s only when it had overwhelming superiority. Not an aircraft I'd like to find myself having a bit of a fight in. Having said that, they didn't have much else, P-40s aside. The only Lightnings used by the RAF - all two or three of them, I forget precisely - were used for target marking by Bomber Command master bombers. They were not officially on the books.
In my honest opinion, it's continued use by the USAAF is due only to the same bull-headed, damn the casualties attitude that kept the USAAF flying daylight bombing missions during 1943, when the losses were prohibitive. The aircraft from that campaign are regarded as being great designs, too. Perhaps something of the respect one has for the men carries over onto their aircraft...