For me an extra dose of that difficulty is due to the fact that the arcade controls simply "feel" slower and more sluggish than the SNES version, which feels a lot smoother or something. It also seems like the hit box on your ship is a little bigger in the arcade version, that and disappearing pixels from time to time really piss me off (like the blob boss in stage 2, when you've shot up the middle a bit and it caves in towards his weakness, even though you don't see those bouncing blobs go through him... they still do and will kill you, so it looks like you're getting hit by nothing).
