Interesting! Just as a data point on the variety of Tinderbox styles, I use the previous/next tab command roughly 1000x as often as I do "close tab." Reason, in my case:
I set up windows with multi-tab layouts, to look at data in different ways that I prefer: Map view in one tab, an outline-agent view in another, then a couple of attribute browser views. Back in the old Tinderbox 5 era of multi-window layouts, I'd have these each in its own window, placed around the screen. Now it's more practical for me to set them up as tab -- and, for me, the point is that I set them up, and then rarely tamper with them.
(As Mark B knows, I keep experimenting with multi-window layouts in TB 7. But for whatever reason I keep encountering a "disappearing window" bug, where the multi-window layout gets boiled down to a single window, with no other damage or corruption to a file. So I've shifted for now to single-window/multi-tab layouts.)
I do sometimes delete a tab, but usually as part of the "incremental formalization" system of Tinderbox, when I have some new idea in mind for laying out data. I am mentioning this not to say it's the right way, but just for compare and contrast on different approaches.
I had a variant of this issue: If I was working in a a multi-window file, hitting Cmd-W (rather than Shift-Cmd-W) would close just one single window -- and in closing it would remove it altogether from the file's layout. (There was no way to Undo that, and my recourse was to recreate the layout by hand or find an old version of the file and copy out the XML governing windows layout.)
I solved this problem with a step you might want to consider. Using the Apple SystemPreferences/Keyboard settings, I changed Cmd-W from this potentially destructive setting to something harmless. (I now have mapped it to "Save.") FWIW.