Well, yea, but...

I am far more libertarian when it comes to zoning laws than most people, so I too think that adding an in-law suite to a house should be perfectly fine, though I do understand why it mostly isn't.  That said, if you want to have them you can't say this:

Cherry Hill ordinances lump "mother-in-law suites" with auto-salvage businesses, junkyards, and heliports as impermissible in residential areas. The township wants to prevent single-family homes from conversion into duplexes or rental apartments, which makes sense. [emphasis added]

Um, no, it doesn't make sense. A house with an in-law suite is a duplex/house with apartment.  If one family owns a house, adds an in-law suite and then sells that house, the new owners can easily rent out the in-law suite as an apartment.  You cannot both want to have in-law suites and not have apartments.  The closest you can come is to limit them somehow (no more than 1 suite, and the size of the suite must account for less than 40% of the total square footage of livable space). 

Also, what about someone who wants to add an in-law suite for down the road, and is hoping that a few years of renters could help to offset the cost before mom/dad move in?

Particularly in more dense areas (cities and close in suburbs) adding an apartment/flat/in-law suite is an excellent idea, but even if it is only serving as the in-law suite for the original owner, it must be available as an apartment for that value to be realized.