The more home pods you have the better your music will sound. I believe they talked about how this device is so aware of it's environment, that it adjusts when there's more than one unit detected to fill the room with great sounds.
The demo has an example of the device being great used independently in the room, versus adjusting when there's two in the same room. Connecting multiple together shouldn't be a problem, and likely what Apple is hoping to bank on. The more people buy the more money in the bank.