[curiouscat]

It is true (I think) that Diastereomers can have differing physical properties but on the other hand enantiomers have identical physical properties.

Firstly, is this accurate. And if so what's a good way to understand why this is so?

Why would Melting Points of D / L forms be identical but different for the meso form?
 

[curiouscat]

I can think of one way to rationalize this: Say I plotted internal atom-atom distances for two enantiomers the tables would look identical. On the other hand, if I plotted those for a pair of diasteromers at least some distances would be different.

For physical properties these interactions matter & hence diasteromers have different physical properties.

Is this the right way to look at this?

[Rutherford]

Take 1,2-dimethylcyclopropane for example. It exist in 1 cis and 2 trans forms. The trans forms are enantiomers while a cis with any trans form represent a diastereomer pair. In crystal form the package in trans alkenes is better than in cis alkenes, hence the difference in melting point. The same situation is here, meaning that the cis and trans differ in this physical property. The packing would be the same for the two trans isomers, only in opposite directions (if it is imagined that way).