I've used real steel parts simply because they're often better quality, cheaper, and sometimes simply not available in airsoft form.
People mention them because they often aren't directly compatible with their airsoft counterpart; I had to spend hours grinding away at an AR charging handle latch to get it to fit the [considerably different] shape of the airsoft part. But given that nobody makes a drop-in tactical latch for airsoft, and since I wanted one, I have no choice. But now I have (or will have -- it still needs finishing and painting) a unique customization that just about no one else has, and to that I say "Neener neener!" :P
Besides, the real steel part was like $15, and if I'd gotten one made for airsoft it would have probably cost about $50.
Bottom line, why use a crappy repro part when you can use a real one.
The same is true, if you dig a bit more, with gear. While a lot of people are happy using cheapo repro gear, the more diehard folks are using real Eagle, Arktis, TT, Paraclete, HSGI, etc. Not cuz they're stopping real bullets or their lives depend on it, but simply because "it's better."
You know the PERFECT example of why people use real steel parts is displayed in the gallery; there's a user (I think his name is "6ft4" or something along those lines) with an absolutely beautiful collection of G36s, and among other things he's using real rails/optics. As you may know, the made-for-airsoft optics on the G36 carry handles are kinda crappy, specially the red dots. So this fellow, using real steel, now has great looking and properly functioning guns.
Last edited by Drake; December 3rd, 2006 at 19:23..