All brands of indexed shift levers can exhibit this behaviour. I've seen it on SunTour, Campagnolo and SRAM. While it surfaces far more often on Shimano units, this is because their production far outnumbers the competition. If Shimano has 1,000 times more units in the field than the competition, then they will also have a lot more failures. This will result in a perceived "notorious" problem, even though their overall failure rate might better than competition.

This issue is just the nature of the grease used as lubricant. All greases will eventually dry out and lose their lubricating properties. Some of these indexed shift levers are approaching 40 years age, so expecting the grease to still perform satisfactorily is asking a lot. Most members buying a C&V bicycle will routinely overhaul the hubs, bottom bracket, headset, pedals, etc. They'll even clean of the old grease from the stem and seat post and apply new grease, to mitigate binding issues. Indexed shift levers use grease too, so why should they be any different?