Not everyone uses only a single miner like that. I mine based on profitability of the coins and use the API and other factors to determine what to mine automatically, then it generates the run command based on the API data. I see the API reporting the best port to use as a more elegant solution, since the server would know better. It would also eliminate the miner needing to sit idle waiting for a timeout before switching.
I'm not sure how many use the API like this but it might encourage its use more to balance the ports.
Aren't these things done within the miner instead? Miners just set failover pools and that's pretty much it, when the first pool:port in your list of pools is not accepting connections anymore your miner just switches to the next one.