Almost nobody in the world needs EVERYTHING that the Mozilla suite includes, and they certainly don't need the codebase for it all loaded into memory all the time. You refer to the separation of tasks between browser and mail client as though it's a bad thing, even comparing it to the separation between browser and mail interfaces in Microsoft applications The truth, of course, is that the MS applications don't separate the stuff much at all, and that's part of the problem: when you load even something as relatively innocuous as Outlook Express, you get the full rendering engine of IE loaded into RAM and most of its interface features (and bugs). While the Mozilla suite isn't nearly that bad, it tends to suck resources a bit more than the independent clients that the Mozilla guys are turning out now.
Of course, there's also the simple fact that the configurability of Firefox is unmatched by any other graphical browser. Between plugins and extensions, you can build a browser application that runs anywhere from highly functional but lightweight to the Mecha-Mozilla of browsers, complete with overgrown lightbulb under its head. Even better, when you don't have some features active, they [b]don't exist on your computer[/b]. K.I.S.S.
Bloat and cruft are the banes of my computing existence. I'll avoid 'em where I can, thanks. The Mozilla suite is an overinflated feature-creep nightmare running a close third to Netscape among major ISP-agnostic browsers.
In addition to all of that, I'll present an example of what's nice about having the separate Firefox browser: I've got a Pentium 233MHz Thinkpad 560X with only 64MB of RAM. I need a good graphical browser on the thing because I use it to access my employer's website when I'm working in the datacenter, so I've got Firefox. For a mail client on the thing, I'm currently using MailX at the command line, and for IRC (to convers with the devs while working on servers) I use irssi, again at the command line. Talk about a small memory footprint. . . .
A Real Linux User uses command line. Heh.
Of course, all of this is from my own point of view. I have different tastes than others. Considering your attachment to LFS, I'm surprised you prefer the Moz suite over Firefox (or even Lynx), but to each their own. I'm sure your reasons for preferring the Moz suite are perfectly valid. They're just not applicable for me, and for my purposes Firefox is as close to a "perfect" browser as I've ever seen.