What Is Virtual Tach Exactly?

Most units can use voltage sense.  Since you didn't mention what unit you hooked up and what car you hooked it up in it really isn't possible to answer your question.

In my professional experiance any car that ever left our bay without a tach wire hooked up came back for cold start issues. 

If your'e referring to DEI's "Virtual Tach", that option is set as the default if you installed a 5701.  So no tach connection was required to start the vehicle.  In Virtual Tach mode, the system looks at the voltage during cranking and uses that as a reference to determine if the vehicle has started after cranking.

"Tachless" modes have become "smarter" in the last decade and are alot more reliable than they have in the past.

A wired tach/coil/injector connection IS better than tachless mode, however.  Monitoring the tach signal can detect an over-rev, among other things.

It's been a few years since I've installed a DEI remote start but back then they had programmable crank times.  After the starter cranked for that set amount of time the unit would look at the voltage and make sure the alternator was spinning (ie higher voltage).  Are you saying they don't do it that way anymore?

I don't believe monitoring the voltage while cranking will give you any feedback whatsoever on if the car is running though, because the starter will load the electrical system down to the point it will be even, or slightly below, the normal resting voltage of the car.

Are there units out yet that have temperature compensated crank times?  I know many newer chips have built in temperature sensors - it wouldn't take much to add a tenth or three on to the crank time if the temp gets below a certain point.  That's what always got us up here in Ohio, voltage works great in the summer, won't crank the car long enough in the winter.