How are others dealing with this?

If I provide HDV as a source for Compessor the results are fine when downconverting to 16:9 letterbox DVD.

If I provide EX1 video as a source, Compressor treats it just like HDV (1440x1080) and stretches it.

Is there a trick to making the aspect correct for EX1 video (1920x1080)?

No problem here at all. Using Compressor 3.0.5. Square pixels in, square pixels out.

You don't mention your version of Compressor setting or preset used or how you're viewing the results so there's not much help I can provide otherwise.

If you use Compressor to downconvert to 4:3 SD, then you need to go to Inspector>Output Image Inset (Padding) and select Padding: 16x9 1.78:1. That will letterbox the image so it does get stretched.