It's not that you can't plug a motorcycle tire. Its more of a safety issue. Even on cars, some plugs will leak. The question is do you want to risk that on a motorcycle for any longer than you have to?
In a pinch, plug it, get home and order a new tire. If you must, ride it plugged until the new tire arrives. But, why test faith for the cost of a new tire by riding on the plug until the tire wears?
I think that's what everyone is saying.