Did the development of Excel 2003 not benefit from all of the work done in the previous versions? Even if it had been a from-scratch rewrite, which it was not, it would have still benefited from the design iteration and experience of the development team in solving the same problems in previous versions. Excel 2003 was not a first-release that was suddenly a refined product that would be useful for years without additional maintenance. I used Excel a few times in the 80s, and regularly through the 90s and early 2000s on Macs and Windows and wrote quite a bit of VBA for them professionally.
What part of my claim is bizarre? My claim is simply that Word and Excel had 20 years of history prior to the 2003 release. Your claim that it was originally written on a different OS is not really a reasonable counter-argument. The Windows version of Excel came out 2 years after the Mac version, so that only knocks the history of the "Windows" version down to 16 years.
By the same logic someone could claim that 1985 Excel was in fact based on the preceding 20 years of mainframe and minicomputer software and the very first spreadsheet-esque programs.
And that those were in turn based on the ideas of Von Neuman & co. from 1945 of tabulating numbers efficiently, and so on and so forth in roughly equivalent leaps all the way back to the first abacus.
It's so reductive of a perspective that it's self-defeating, since no human being, including you, could ever actually comprehend the entirety of technological development, or even just the post-1945 developments.
I think it is a pretty clear line between attributing the quality of a piece of software to two decades of prior development at the same company, with its own continuity of developers and institutional knowledge, as opposed to the general benefits all software gains from the industry advances it builds upon.
No it's not a clear line at all. In fact Lotus 1-2-3 was literally the direct predecessor from IBM in terms of everything but the brand name and some design choices.
What part of my claim is bizarre? My claim is simply that Word and Excel had 20 years of history prior to the 2003 release. Your claim that it was originally written on a different OS is not really a reasonable counter-argument. The Windows version of Excel came out 2 years after the Mac version, so that only knocks the history of the "Windows" version down to 16 years.