Taking another look at the linode site I can definitely see where the confusion might come in as it's difficult to find any indication that costs are calculated daily. However I did find the following, again from the FAQ:
Can I upgrade my Linode?
[...]
Removing resources pro-rates the balance of the month back to your account so you only pay for the time you've used them.
Edit: I've just gone into my linode account and the removal link does give you a figure for how much you'll get back. You pay for a month in advance but if you don't need the full month you can remove the linode and get your money back for the time remaining.
Can I upgrade my Linode?
[...]
Removing resources pro-rates the balance of the month back to your account so you only pay for the time you've used them.
Edit: I've just gone into my linode account and the removal link does give you a figure for how much you'll get back. You pay for a month in advance but if you don't need the full month you can remove the linode and get your money back for the time remaining.