But they're completely different...
One focuses on the party- the other on controlling one person.
Or a party of one.
Actually, that's single most important difference, but I wouldn't consider it *that* important as there are blobbers that permit one character parties, and goig solo is one of two logical directions of improvement for an RT blobber - the other being going TB.
One thrives off its inventory management and exploration, the other typically focuses on combat exclusively.
Really? Because I've seen FPS games with a lot of inventory management, exploration is nearly ubiquitous in FPS games (other than modern cinefaggic corridor popamoles, that is), and blobbers are not exactly known for their non-combat focus.
And that's even if we only consider pure FPS. What about RPGs (TES, UU), adventures (AzT), or horrors (Penumbra, Amnesia) based on FPS style movement, presentation and controls?
One has step-based movement, the other is free.
Actually, that's sort of the crux of the problem here.
You see, early FPS games - I'm speaking of truly ancient ones - were RT step based with tiles and 90 degree rotations.
Then the system was adopted by RPGs and generally did a lot of back and forth between both genres while being refined.
Some games focused on refining the RPG aspects and party based tactics and improving movement and presentation was of relatively low priority to them. Others focused on both, trying to create a comprehensive experience - we're speaking of games like UU or TES. Some were result of discovery that players like running around killing monsters, which resulted in throwing out RPG elements and constructing games focusing on simplistic but dynamic combat first and foremost - so we've had Wolf3D and Doom, but there were games reintroducing complexity in one form or another into the FPS genre as well, sometimes moving back towards RPGs, sometimes merging with sims or adventures, and sometimes doing evewn weirder stuff.
Even some TB games eventually adopted free movement and were better for it.
So you see, ability to move and look freely is natural and pretty much unquestionable refinement of step based movement and view.
A case could be made for retaining step based in a TB because it would allow much shorter travel times (a flimsy justification considering all the drawbacks, but a justification nevertheless), but in RT you need to limit the speed anyway, or you are designing a broken game, so there is no possible rationale for keeping step based movement in an RT game if the technology allows you to get rid of it.
It's not pixel art or anything else with actual unique artistic value.
RT blobbers can be viewed as either failed FPS games where you have to fumble around menus or icons with your cursor in order to hit something and the pace is slowed accordingly to make the game playable, or failed TB blobbers where in depth mechanics and menus are necessarily limited by having to be navigated in RT.