This site has some interesting tidbits about Williams arcade machines, including a multi-game cabinet that runs real (not emulated) versions of Joust, Sinistar, Robotron, Splat, and Bubbles.
Why do this? Well at the time (and possibly today as well) there were slight differences in blitter operations between the real machines and the emulated versions. Here's an excerpt:
In older versions of MAME and in several xx-in-one boards, blits happen pretty much instantaneously, unlike the real games where the Special Chips have a maximum throughput of 1 MB/second (not counting the time it takes to write to the registers to start the blit). This results in games that appear normal at the beginning levels, but become much harder at the later levels. Robotron can have so many enemies on screen at once that all cannot be moved in one video frame. So the game moves as many as possible, then moves the rest in the next frame. With an "instantaneous blitter", all the enemies can be moved in one video frame, making the game play much faster.
About 13% of the blits had different results in MAME than on the real game, and about 11% of the blits took a different amount of time in MAME than on the real game. I'm sure that these blits represent a very small proportion of blits done in actual game play, but they may still contribute to game play anomalies.
Defender and Stargate are included in the cabinet too, although those two don't actually implement blitter code.