Touted as equivalent by Dell sales, by Dell warranty service, or by your IT people?

The exterior dimensions are close enough to seem equivalent for me (and while not nearly as thin or light as as the pre-Ultrabook Lenovo T400s-T430s, the E6430s and the E6440 are the next-most-compact chassis on a full-power-process 14" machines that I'm aware of.)

Are the other differences in configuration that might have a big impact on weight, like the number of battery cells, and/or one has an optical drive rather than a spacer?

Is that their "weight from" in the specs, or as you're measuring it?

By the same, is that by benchmark, or nominal clock speed? Because in practice, the processor in the E6440 would have to be clocked a whole lot lower to be the same speed.

Dell stopped offering one this genertion, although they have ultrabooks (which may or may not be as fast as the old one) which are even lighter and thinner still at the same footprint.

That would be the Ultrabook models. The E7440 would be a much better option from a weight perspective, although while thin it's still a little broader as it is a 14" model. The XPS 13 would be an even better option from a space/weight perspective (especially the new 2015 model, which is TINY for a 13" machine) but it gives up docking and other enterprise features, and is pricy.

Depending on the processor you have in the E6320, and which ultrabook processor you were to get, the ultrabook processor could be anything from substantially slower to slightly faster.

For some people, that would be a good trade-off. After 2 generations of quad-core 14" machines from Dell, they dropped having a 14" machine with a quad-core processor for this generation.

I think the business case is more a matter of keeping number of models down; 13" has become the defacto standard size for consumer Ultrabooks (copying the MacBook Air) and the need to have model to compete with that seems to have crowded out the 13" non-ultrabook models.

Add in the popularity in business of the 14" ultrabooks (although Dell's earlier model, the E6430u was kind of reviled) and 13" is pretty much just a consumer size now (or for crossover mainly-consumer models.)

Fundamentally, there's relatively little that's happened in the technology to make an equivalent 13" laptop from 2014 any lighter and smaller than a 13" laptop from 2011; in 2011, like today, you could have a very thin/light 13" one like the MacBook Air (or today's Air, or Ultrabooks) using a ultra-low-voltage CPU and probably with some memory limits, or you could have a full-size 13" laptop with a much more powerful processor for the generation.

Dell switched which one their 13" machine was from the ultra-light [for the time] E4300/E4310 in the prior two generations to a merely small E6320/E6330. They then changed it back with this generation.

The only thing that's changed in that time is that the speeds have gone up (pretty considerably from the 2nd to 3rd generation Core i, less so on the 3rd to 4th) and the battery life of the processor has gotten better (although it's often eaten up by brighter and/or higher resolution screens, and higher power/faster wireless cards.) For many people, that's made the ULV processor in what are now called (and were not yet in 2011 coined as) Ultrabooks.

One of very few companies I know of who opted for that size, although I think that's what our Dell sales rep carried back then.