Wired style is simply wrong: E-mail may be e-mail, but it is not email (or ebusiness or econsulting). There aren’t many single-letter prefixes in English (a- is one, as in ahistorical).
According to my Canadian Oxford, e- can be a variant of ex- and also has the sense of “denoting anything in an electronic state.” They don’t capitalize either sense, but they write both with a hyphen, as they must be written.
If you disagree, read the following excerpt out loud and tell me if you don’t make a mistake:
In fact, the only group resistant to ebooks is consumers. Many consumers, never having actually seen or touched a dedicated ereader before, mistakenly think that the only way to read an ebook is on your computer or cell phone.