There are a lot more strains of liquid yeast. If you want to make a true-to-style beer it's more likely that you'll be able to recreate that with the right yeast. For example, there are British Ale dry yeast varieties such as S-04, Nottingham, Windsor, CML Four, CML Beoir, CML Midland, Gervin, MJ have a few too. These are pretty much it with several being very similar strains from different suppliers. You're looking at about 4-5 different strains in truth.
Compare that to Wyeast liquid strains. Alone, Wyeast have 1028 London, 1084 Irish, 1098 British, 1099 Whitbread, 1187 Ringwood, 1203 Burton IPA, 1275 Thames Valley, 1318 London Ale III, 1335 British Ale II, 1469 West Yorkshire, 1728 Scottish, 1768 English Special, 1882 Thames Valley dry, 1968 ESB. That's a lot more choice.
I use dry yeast almost exclusively because I'm happy to be roughly in the ballpark with yeast flavour. I have also brewed recipes that will be OK with dry yeast. On the odd occasion I've used liquid (3068 Weihenstephan Weizen) it took the beer and flavour complexity to a different level.
Dry yeast manufacturing is an expensive business so only a limited range of popular strains will ever be produced. I would also guess that certain strains are chosen because they lend themselves well to the drying process, rather than for their outright flavour.
Some people produce great beers with dry yeast and many commercial breweries use it because it's simple and consistent. Nothing wrong with dry yeast if it suits your recipe and brewing style.