Honestly? Excel is a premier application, that microsoft spends extreme amounts of effort making great. There isn't a FOSS spreadsheet program that really comes close. It's not that there can't be, it's that the excel line is moving faster forward than current FOSS spreadsheet projects.
Perhaps its a 'purest' mentality, but if you're going to learn how to use a spreadsheet app, may as well learn the one that is most well known and widely used. As the video shows, Google Apps, Numbers, and the rest of them really are missing core features.
Joel didn't even get into VBA scripting - thats some advanced stuff that once you realize you need it, but you're stuck in Google Apps...... well, maybe this crowd is smart enough just to make a web app to solve the issue haha! Myself? I stick to Excel.
It's not any more purist than sticking to FOSS :)
There is also the spreadsheet support in Emacs org-mode.
Go to Tools, Options, LibreOffice Calc, Formula and select "Excel R1C1" in the Formula syntax dropdown menu.
In R1C1 notation it's obvious because the formula doesn't change. In normal notation the exact same thing happens under the hood, but the cell references you're seeing change.
I recently had to use a spreadsheet for a first time in a few years, and LO Calc seemed to be dramatically better than OOo Calc back when I last used it.
This is really a shame, because of Gnumeric's history. It was (along with Gimp) one of the very first GTK applications, and present at the beginning of the Gnome desktop suite.