Yeah, however 'perfect' the implementation was or wasn't (as was argued on ANN over the Wikipedia entry not too long ago), it was certainly the first 'home machine' to expect and prepare for the modern use-case from the start. Or if not 'the first' (I keep waiting for some rare home UNIX box that sold three units in 1979 to come up and bite me in the ***), the first to do it in a fashion eminently recognizable as "the way everyone does it today."
As much as I enjoy jumping on the Amiga bandwagon I'm afraid I can't in this case.
OS-9 was the first in 1983 for the 68000, and actually was multitasking pre-emptively in 1980 on 8-bit systems.
