Someone could, otherwise, buy a thing with the word Arduino on it and be confused as to why its not working the way they expect or is incompatible with the software and then blame Arduino when really its that the clone is not compatible.
just to argue that point on a purely objective level 
, I think it's FUD, as there aren't any non-compatible Arduino products that I know of. Anyone who buys a Barebones Arduino (which uses the name but doesn't match the specs of the original) knows they are getting a slimmed-down version of the original, and that the product has been engineered to be compatible with Arudino software. Buyers don't turn around and blame anyone... In fact it seems like Paul's use of the Arduino name and his derivative design works just fine in practice! No collapse of the Arduino empire in sight!
By contrast, the VAST majority of complaints/ compatibility questions in the forum are about the team-produced, officially sanctioned Arduino NG, Arduino BT or Diecimila. Yes they have sold a lot more of those, but still, You would be hard pressed ot find complaint threads about the Barebones.
You could actually make a pretty reasonable argument that Paul should be worried about the Arduino problems turning people off of the Barebones! ;D OK I meant that just in principle.
D