. . most of the rest of us are not connected to "the very definition of VT220". Linux in particular has ratty termcap/terminfo definitions that need to be fixed before use.
My favorite item is that the lower function keys use completely different coding than the higher function keys, and whether the transition is at F4 or F5 or whatever seems a matter of opinion, but some programmers use one or the other encoding all the way through. Which one appears also to be a matter of opinion.
Anyway, next time I mess with this stuff I'll take a look at PuTTY and see what I think of it. By the way, KoalaTerm makes full use of available TrueType fonts, which many emulators do not.