To relate this back to the equation editing problem, the problem with any TeX-based way is that you won't get identical layout from one platform to another. TeX (whichever flavor you're talking about) is designed to maximize the quality of the output for each given platform, but that sacrifices some aspects of layout compatibility.Here, Mr Schaut, you are happily wrong :-) TeX and LaTeX cleverly outsource the work of device- and operating system-independent document rendering; they merely specify the document's internal structure. Once a TeX processing system has turned the document into a PostScript or PDF file, you can merrily distribute it anywhere you want with full assurance that the rendering will be inviolate, down to the last full stop on the last line of each paragraph.
Suppose, for example, you have two people working on a paper. One uses a Windows computer, the other uses a Macintosh. Should that paper include a rather lengthy equation, there's a good chance that the equation might fit on one line when the document is opened on the Mac yet not fit on one line when the document is opened on the Windows computer.
And of course, unless I'm missing something here, any plain LaTeX source files will compile to the exact same PDF file whether it's on Windows or the Mac; that's a given, because the processing that TeX applies to the source file is the same regardless of operating system.
Of course, there is the entirely separate issue of distributing LaTeX source files or DVI files of your documents; but given all the potential incompatibilities you can face there, why even bother to distribute anything other than PDFs? LaTeX + PDF is the only sane way to go.