by bells and whistles I mean things like the spectrum emulators automatically typing all the loading stuff you need if you drag and drop an image on them, then catching common loaders and hleing the entire loading process so it doesn't really load how the real system would load it, but simulate the whole process to load in a fraction of a second, fake 256 colour modes, and sliders to tweak every aspect of a system timing to values you'd never see used in reality.
stuff like that isn't 'emulation' at least not the HLEing of all the loaders because you're specifically NOT running all the original code the way the systems would if you start doing things like that. scripting the inputs isn't so bad, and could potentially be programmed into the software lists, but the 256 colour modes are something made entirely for emulation and never existed in reality (well not unless somebody has since built a real machine capable of them)
a lot of the computer and console emulators are similar like this, with fake enhancements, high resolution Playstation graphics is another common example, where everything is rendered as if the original playstation had a 1920x1200 widescreen resolution, with polygons smoothed out etc. If you emulate it properly most kids today think the graphics kinda suck, but MESS will only emulate it properly.
it wasn't really a statement about the arcade side as much, MAME still doesn't offer such enhancements, but there are less 'alternative' arcade emus, and nobody is going to spend their time doing artificial enhancments for platforms with only a single game ;-) NeoGeo did see fake transparencies and stuff in Nebula / Kawaks but people got bored of that gimmick rather quickly. Zinc does hi-res PSX but only runs a fraction of the PSX based titles MAME does, so people quickly stopped caring about it.
so yeah, MAME is still 'no frills' but you don't really need them, if the emulation is correct it does what it's meant to do and that's that.