That's not an intrinsic part of TCP/IP the protocol is irrelevant. You are right though it should be possible to reroute the traffic either automatically or manually to work round the break. Sounds like penny pinching to me.
The thing is though that this is what you get for using low cost or free services. What's the SLA on Yahoo! Mail? Customers complaining probably never checked when they signed up. Guaranteed percentage uptime? Guaranteed time to restore service? Compensation for outages? Bet there aren't any of those in the contract.