The abstract doesn't define the patent. The claims are what defines the patent, in combination with the notes in the patent file which can often limit the claims even further.
Yahoo is claiming a specific method of seamlessly converting an instant message communication into an email one, not the general concept. Claim 1 narrows the claims from that general case immediately.
IMHO the linked article misunderstood what this is all about.
I think it's more the "Reply to this thread by replying to this email" facebook does when you receive a message notification.
