You may not be aware that Ctrl-I toggles the mode of new text, not just selected text. I think that poster was saying this:
If you're writing a new sentence in MSWord, you type "Emphasize words <Ctrl-I>like this<Ctrl-I>."
If you write a new sentence in Markdown, you type "Emphasize words *like this*."
The keys are neighbors even, at least in a US keyboard layout, so there is not a reason most US users would say it's "faster" to type * than Ctrl-I. (And if other layout users disagree, okay, but I don't think that was in the scope of the original point.)
If you're writing a new sentence in MSWord, you type "Emphasize words <Ctrl-I>like this<Ctrl-I>."
If you write a new sentence in Markdown, you type "Emphasize words *like this*."
The keys are neighbors even, at least in a US keyboard layout, so there is not a reason most US users would say it's "faster" to type * than Ctrl-I. (And if other layout users disagree, okay, but I don't think that was in the scope of the original point.)