Passenger car diaphragms: simple rubber tubes-why?

[SouthernRailway]

I see that NY-area commuter railroads' car diaphragms consist of rubber tubes such as these:

http://www.mwrail.com

Before coming to NY, I recall that diaphragms were usually metal/more complex ones, as in the second photo here:

http://www.americanlimitedmodels.com/ol ... oducts.htm

Yes, this is a totally nit-picky questions, but why the difference? I'd assume that the rubber ones are cheaper, but are they used mostly by commuter railroads since people don't walk between cars as much as on a longer-distance train, which would have a more complex diaphragm to provide more protection from the elements? Or are the rubber tubed ones the new style for all new equipment, regardless of type of passenger train?

Thanks.

[DutchRailnut]

The rubber once are easier to maintain, compatible with all cars even in mixed (freight) consist.
and are used all over Europe too, The Metal once will sideline a car if damaged, the rubber once do not.

[mtuandrew]

Moderator's Note: Moved to the General Discussion: Locomotives, Rolling Stock & Equipment forum.