Astrocade Emulation MAME Speed Difference

Based on these two facts of running "Grandfather Clock" loaded from tape (see early post in this thread):

1) Real Hardware - AstroBASIC: 1 Minute = 38 seconds in real time.
2) Emulation - AstroBASIC: 1 Minute = 55 seconds in real time.

If I've done my math right here, then 55/38 = 1.4474.

This means real hardware runs "Grandfather Glock" about 1.45 times faster than it runs under MAME emulation. I noticed this real hardware vs. emulation speed difference when I loaded "The Gate Escape" from tape. I'm pretty shocked by this speed difference, as I don't remember seeing a speed difference like this between other non-BASIC cartridges.

Any ideas of why this speed difference is happening?