If you truly want to help people who think that Thunderbird comes with an email account, you should provide them with an easy explanation between IMAP and POP and offer them a choice between a free IMAP account (for example GMail) and a free POP account (for example lavabit). Right now this is just a shameless money making scheme.
In reply to your reply (rather late). Both GMail and Lavabit do NOT mine the contents of your mails, nor do they add or change the contents or subject lines. Which was the point I was trying to make; there are very good, quality free alternatives for both POP and IMAP without the need to pay.
We believe that some of our users would appreciate the opportunity to pay for a personal, private email account instead of getting a "free" account in which the contents of their email are mined to sell advertising targeted at them. Of course, many won't, so we are also working on integrating with several of the top ad-supported email providers. Sadly, that work hasn't gone as swiftly as we had hoped it would, but you can expect to see free email accounts listed alongside paid accounts in a future update.