Zach,
Ok, I just walked over to the skil engineers desk who is responsible for the Skil 77 and Mag 77. He also had the Bosch one at his desk.
Skil 77 : 16 lbs, stampled steel base, non mag housing, 45 degree side adjustment, 13 amp rating that is in the process of changing to 15 (only required changing lead wire size to get that rating), no soft grip on handle.
Skil Mag 77: 14 lbs, stamped aluminum base, Mag housing, 45 degree side adjustment, 13 amp rating that is in the process of changing to 15 (only required changing lead wire size to get that rating), no soft grip on handle, available with hanger hook.
Bosch : 14lbs, cast Mag base, Mag housing, 50 degree side adjustment, 15 amp rating, soft grip on the handle, has hanger hook.

Amp rating of a tool: Although a tool may have an amp rating, you usually are not pulling that many amps when actually using the tool. Amp rating is determined by a UL temperature rise test of the tool and motor. It's only allowed to rise a certain number of degrees when the tool is loaded to the test amps, like 15amps for example, in a certain, set time period. You can test a tool and try to get it to pass for a higher rating as long as you can pass without going over the temp rise limit. Amp ratings are often used for marketing purposes. While they are a measure of how well a tool can remove heat or stay cool, it may not make one tool significantly better than another if the operating current is much lower. For example if a tool is rated at 13 and another at 15, but the tools basically operate at 6amps (this is just a made up number). The tools may not have any difference all other things being equal. If the operating point was closer to the rating, well then there could be some (I say some) difference in brush life. My point is that I wouldn't put too much weight in the 2 amp rating difference. Often the same tool can pass a higher amp rating with a minor change, like wire size increase (reduces resistivity and thus heat loss, but increases cost). I will go find out what the normal current draw is for those saws.