Everyone? Literally everyone? Your mother, your brother, your gran, your 2 year old nephew? As you know that is obviously a no, I doubt you meant that. But that you clearly don't mean it literally does raise the question:
What is it you mean by 'everyone'?
What is your target audience?
If you're targeting digitally adept 20-somethings with some sort of an application that connects with facebook...then yes, it is probably a fairly safe assumption that pretty much everyone has an email address.
If you're looking at the general public as a whole though...Then there are a lot of adults who don't have an email address. Even many who have no trouble using the internet as part of their daily life. In my studies I've came across a lot of people like this. They're generally a little bit older, 40/50+, and as far as account-driven sites are concerned they stick to only one or two (facebook and amazon are the usual). Often they technically have an email address (set up for them usually), but never use it and have totally forgot how to access it. Other times they merely borrowed the email address of a more digital relative to sign up.
Grant's point about considering whether you actually need it or not is also very valid. When people are asked to enter their email address there is a little bit of a recoil and a push away from signing up, a sort of "Uh oh, here comes more spam" or "Great, so now I'll have to go and check for one of those confirmation emails, pfff".