You think a product manager was in any way involved with a function signature. I'm fairly certain this didn't come up in more detail than a requirement: "We need to add a way to call a macro...". And the story as told by the PM would be "...and so the engineers added a way".
I've worked with a bunch of PMs on technical products, APIs, etc. and I've rarely met anyone discussing that level of detail or willing or able to make such a decision.
The engineers chose a way that worked and it's likely the best way supported at the time, given the other comments I've read here on HN.
Joel Spolsky was the program manager (true, not product manager) when VBA was added to Excel. He talks about it on his blog.
"As a program manager at Microsoft, I designed the Visual Basic (VBA) strategy for Excel and completely speced out, to the smallest detail, how VBA should be implemented in Excel."
