Kai, I don't find the multi-key-closure problem very common with keypads. These are normally addressed with one finger, particularly in vertically mounted keypads as one finds on test equipment and wall-mounted appliances, e.g. microwave oven, telephones, stereo equipment, etc.

If one "played" a keypad with multiple closures, one could, of course, encode more values with fewer keys. This has been tried, with technical success, but was a market failure. The market has determined that the CONTROL, ALT, and SHIFT keys are enough to play simultaneously. If one really had to use multiple keys, as in the case of those particular ones, specific allocation of matrix space could be made, if necessary, and it would save the diodes. I believe, and this is only MY opinion, that, unless one is faced with a dearth of port pins, matrix expansion, i.e. letting the "special" keys live on their own row, is a better way to deal with this eventuality.

RE