Compression and loudness are not the same thing. Compression limits the dynamic range between the loudest sound and the quietest sound. It's useful for making something work in a noisy environment (like your car), but its robs music of the emotional shock value of changing dynamics. Nonetheless, for rock music, I've heard some very good recordings that make limited use of compression.

Turning up the base level to make the entire recording louder is an old trick done to seemingly make the music "pop" compared to other recordings. This is often done in the mastering stage, so the recording will sound fine to the band during mixing, but the peaks get clipped when they exceed the CD's dynamic range during mastering. Sadly, Coverdale seems to like the idea of mastering everything hot like this. All the recent re-releases suffer from "too loud" mastering, and all of them sound worse than the original CD issues.

The Deluxe edition of the 1987 album is unlistenable while the more recent remasters are slightly better. I think both GTBB and Forevermore suffer some from the mastering with Forevermore sounding a bit better than GTBB.