The A-mount Alphas are not mirrorless. They have a semi-transparent, non-moving mirror that steals about 1/3 of a stop to send light to the AF sensor. It gives most of the advantages of the DSLRs (phase-detect AF, but that's creeping into higher-photosite-density mirrorless cameras) while making live view and continuous AF much less complicated.

That's why Sony refers to them as "SLT" cameras and not SLR.

You'd be just as well served by comparing a $900 Nikon (D7[12]00?) or Canon DSLR to the D4. If you can't justify the difference between, let's say, a D600 and a D4, then it's moot anyway. I imagine the D4 compares quite favorably to the HST and Kepler on many axes as well. :-)