Forgot the punchline
MSHMTL is an HTML page viewer. Because it's a component and not an application, anybody is free to use it in their own software. You can build your own Web browser in a few lines of code, add HTML help to a program, even replace the Soviet-style grey dialog boxes in programs with a rich, colorful, Web-style interface. Norton AntiVirus and several other programs I've encountered use HTML interfaces instead of the old-fashioned Windows interface, and they're a pleasure to use.
And that, Bowser, is why you couldn't install the Hallmark program without an IE installation--it must be using MSHML to create a nice interface.