Based on an hour or so of research, it seems that multiple MSXML multiples are needed, at least in the case of ver. 3. It may be possible to uninstall or delete versions prior to 3; they are in the same 8. version series.
I have seen indications that 3 contains features needed to support some xml applications which have not been incorporated in later versions. The applications use features which have been deprecated (love that word, the ultimate in bureacratese in high tech, bureacratic in every respect, but too rarified for use in actual bureaucracies!) in later versions of msxml.
Which duplicative, multiple msxml versions can be safely uninstalled or deleted? Is there a source that describes the relationships of the different version, and how that impacts on decisions about which should be axed?
Here are the versions MS's "XMLVersion OCX" produced for one computer:
MSXML 2.5 Non-SidebySide Registration Version 8.0.6730.0 D:\WINDOWS\System32\msxml.dll
MSXML 2.6 SP3 8.30.8709.0 D:\WINDOWS\System32\msxml2.dll
MSXML 3.0 Unknown Release 8.70.1113.0 D:\WINDOWS\System32\msxml3.dll
MSXML 4.0 Unknown Release 4.20.9841.0 D:\WINDOWS\System32\msxml4.dll
MSXML 5.0 is not installed Not Applicable Not Applicable
MSXML 6.0 is not installed Not Applicable Not Applicable
WINHTTP5 is not installed Not Applicable Not Applicable
WINHTTP5.1 Unknown Release 5.1.2600.1557 D:\WINDOWS\system32\winhttp.dll
