liudr:
Since a simple button only costs a few cents (in US) but a button with the proper plunger (actuator) for a cap costs ten times more (digikey), I would imagine most LCD shields are made with the cheaper ones.
I have subsequently bought a stack of every length that Tayda stocks, but the reality is since this project I've opted to avoid shields and run with an independent display with switches mounted through the enclosure just because it's so much easier, more flexible for the layout, and of course you can avoid trapping the Arduino and run with a cheaper board with an ATmega on it too.
liudr:
Their purposes are more academic than practical
Unfortunately that bit is clear. It's not just these LCD shields either. Since moving to bare ATmegas and ATtinies for the final versions of project I have found a lot of display modules have their cable headers on the top side which means they need to be moved to the underside to use an enclosure. There sure must be a lot of naked projects out there 
Geoff