Its also about revenue protection, ProTools as software only is vulnerable, with the hardware it becomes almost impossible to hack.
Plus the quality of the Focusrite mic amps is way better than Macs own audio-input, and you get digital in/out. The main drawback is the lack of physical inputs for mulit-track recording, stereo is fine for foley/location and overdubbing, but its not enough for a proper MT drum recording.
The use of a multitrack in/out expands any system massively, check out MOTUs 828 systems, pricey but excellent.
The M-Box is excellent for the price, and ProTools sounds like the system for your needs, Logic will do the job just as well, but if you dont need the MIDI itsa steep learning curve.
The chances of a free OSX ProTools is currently slim.