PayPal eCheck Confusion

I bought my wife a replacement cell phone off eBay yesterday (Verizon wanted $159 for their lowest-end phone; this was $20 and can sync with bitpim) and when I sent my payment it went through as an eCheck. Afterwards I got the message that it will take 6 days to clear, and unlike a real check there’s no way to stop payment on it (so I could send an alternate payment).

Well, that got me in trouble with the wife, but it was also really surprising as I always use an Instant Transfer for Paypal. Why did it ignore my default payment method?
Long story short: an Instant Transfer is guaranteed by a credit card on the account and the old card had expired. I updated the expiration date and Instant Transfer came back.

Paypal loses big points for knowing that Instant Transfer is my default payment method, knowing that my credit card is expired, and not asking me to update the expiration date.
My guess is they make more money on the float of an eCheck. Since electronic clearing went into effect, there’s no reason it should take PayPal 6 days to clear any kind of check. I’ll keep an eye on when it leaves my bank account and when the seller gets paid.