Right, but chile is the correct Spanish spelling, and the word comes from Mexican Spanish, so it's the most etymologically correct spelling. The Spanish word comes from the Nahuatl language of course, but we can't exactly spell it their way because Nahuatl doesn't use the latin alphabet. If we're going to spell it "chili" or "chilli" then why don't we just anglicise jalapeño and habanero and spell them "hallapainyo" and "abbanairo" while we're at it? Botanists and chefs almost universally use the "chile" spelling, and so does The Chile Pepper Institute. Unfortunately we're never going to get rid of that pepper tag along, Columbus really screwed us on that one. And "Indian" too. I don't know how many times I've said "Indian" as in people/food from India and people thought I was referring to "Native American". :o
To me, chile is a fruit that grows on plants of the capsicum genus, chili is a southwestern US stew made from chiles and meat. Chile powder is ground chiles, while chili powder is a seasoning mix used to make chili. And "Chilli" is a just a strange, funny looking word that Britains use, that I had no idea even existed until I started searching the internet for information on chiles. Yeah I know I'm picking nits, but it's all in fun.