Despite the fact that this guy is obviously a jerk and approaching the whole thing in a completely wrongheaded way, there is a legitimate point at the core of all of this nonsense.
The cabs that are sold on ebay and elsewhere are most definitely advertising on the ability to play pirated ROMS. Virtually every MAME capable cabinet on ebay loudly proclaims its ability to play THOUSANDS of arcade and console games. Nowhere on the page will it give the caveat that to play thousands of games, you should own thousands of JAMMA boards and cartidges and have your own personal ROM extractor. I doubt a cabinet has ever been purchased by someone who did not put at least several hundred illegal roms on it within a day of getting it.
Imagine if MAME existed but roms were somehow only available to legal owners. Would people pay $2000 for a cabinet that could only play a dozen or so legal games? Almost certainly not. The Ultracade is being undercut by competitors who are tacitly relying on theft to complete the products that they are selling. They don't have to say "Here's where to go get those 10,000 ROMS I mentioned" they know people will be able to find a .torrent or use other P2P. In fact, even if the roms were available at say, $30 per, this would still cripple the market for MAME cabinets.
I for one will fully admit to the fact that I'm building my cabinet for the exclusive purpose of playing ROMS that I have no legal right to whatsoever. I don't own a single original board, nor do I plan to. If MAME weren't available I might someday (not now, I don't have the cash) consider buying an Ultracade or similar multi-game cabinet, but with the ROMs available, there's no way I'd ever buy one.
Now does this mean that he's entitled to take the legal steps he's taking? Almost certainly not. However, his point that he is competing with stolen goods is legitimate.