That whole wheel art code is made by omegaman and it's copied from robospin theme.
I've asked omegaman if he can change the code to display game name if the wheel art is missing and he made (a valid) point that you just have to men up and find wheel graphics for all your games - if you want to use that wheel. I'm completely agree with him (plus it's a lot of work). That missing wheel art icon should be only temporary indicator what is missing so you can hunt it down.
But (and this is a big but) in omegaman's theme you can choose simple list instead of wheel selector (as an option).
I've decided not to use the list because:
a) I'm using only mame - so there is no problem with collecting all wheel art (now I know that for other emu it doesn't look that great)
b) I have fairly small set of games - all with wheel graphics
But since it is a problem for other users I'm gonna add text gamelist as an option in next revision.
When? I don't know yet since I'm currently really really busy with making the whole set of designs for VR arcade gamehouse - fotoshoot, website, collaterals, posters, etc. and it's a lot of work with a tight deadline (end of this month).
But I'll add it - I promise.