I used Backgammon and TI-Chess 4.00 as the testcases.

Which is, by all measurements, a too small test suite.

I consider it much more important to test that the games still work

Which you did, but it didn't mean much, given the dismal size of the test suite.



Your reply makes me think that you understood the following paragraph

If you had an automated test suite of a couple dozen programs of different types, you'd much more easily get an idea of the strengths and weaknesses of a new GCC version. Making such an automated test suite is no problem, because "disk space is cheap", right ?

was referring to a TIEmu test suite.
It ain't
This paragraph, and the surrounding paragraphs between two quotes of yours, is referring to a compiler test suite (run the building process and see what the compiler yields size-wise)

And it's hard to automatically verify that TI-Chess can still play chess.

Definitely