There are many engineers who feel that plug-ins can't quite achieve the same sounds as their analog counterparts, moreso with compressors than with EQ or delay/modulation effects. It's an ongoing argument that will probably never die.
In my experience many/most people fail blind tests comparing modern plugs and hardware, so take that with a grain of salt.
In my opinion there are slight differences, but it's more of a subjective, negligible difference than the "night and day" difference that many people proclaim it is. It's also worth pointing out that a pair of analog units will rarely sound identical to each other, especially older units - so there are always going to be slight differences when you compare them to plugs.
At the end of the day, it's really up to the engineer to weight the pro and cons and decide what they prefer.