The 60Hz flicker described is a phenomenon called "optical hetrodyne" and it happens when two sources of pulsing light are close to one another in frequency but not exactly matched, and one sees a flicker equal to the difference in the two frequencies. In this case the two frequencies are the 60Hz screen refresh and the 60Hz from flourescent lighting. It is exactly the same phenomenon as one used to see on old direct-view CRT computer monitors with screen refresh near 60Hz. If the two frequencies were well matched, you saw a rolling black bar representing the time when they were out of phase, and a bright bar midway in between when the intensity of both was maximum. If the two frequencies differed by 1Hz or more, you see the entire screen flicker.
Older direct-view CRT TV's avoided flicker by locking the vertical screen refresh to the powerline frequency. This technique is not easily applied to plasma displays. However if you are troubled by flicker you can eliminate it or reduce it greatly by replacing all the room lighting with old-fashioned, inefficient incandescent bulbs. These types of bulbs do not flicker much, compared to the compact flourescent or conventional flourescents used in homes, or the high-pressure mercury vapor bulbs used in big box stores or Best Buy.
Now you know the "other reason" that plasma displays are demo'd in relative darkness in the back of the store. The main one is to suppress reflections, but flicker reduction also happens.
If troubled by flicker, diagnosis of this problem is easy. Turn off all the room lighting one by one, and replace the offending bulbs.