MAME is cool, and its been cool for a long time. I've got a question though: Is MAME just about emulation of historical arcade machines, or is it constantly updating emulation for arcades from the present decade?
There are no hard cut-offs, but contemporary systems are rarely implemented. MAME's focus on accuracy to a low-level degree means that most modern systems would be painfully slow to emulate.
It is, indeed, just a PC with a custom software stack built on top of Windows. Some old-style arcade machines you see in the wild these days are really just PCs, or maybe ARM SBCs, running a library of ROMs via MAME, legally or illegally!