While Mag-Lite wasn't the first to manufacture a solid aluminum light of the nature of it's D and C cell lights, it was the first to produce the same concept in a AA flashlight. With it, they introduced the T1 bi-pin lamp that is so popular in AA lights today. Other manufacturers attempted to borrow the same concepts, such as Brinkmann and Streamlight. Legal action was quickly initiated against them, so, any follow-up products of the same nature had to be made with a view to non-patent and non-trademark infringement.
It's interesting that word got out that Mag-Lite would be introducting a single AAA light. Before they did though, others tried to be the first to produce a single AAA and AA aluminum flashlight. What they weren't counting on was the departure from the larger circumferenced head when Mag-Lite produced its Solitaire flashlight. The large headed lights from the other manufacturers pretty well fizzled, and the Solitaire basically cornered the market for single AAA flashlights. Today, of course, we know new technology has all but placed that bit of history making innovation on a steady path of obsolescence.