>>372715652
It's more to differentiate the gameplay. When people hear STALKER they expect human NPCs, factions, mutand hunting and comfy campfires then get butthurt when it isn't like that. 
On the surface ITR is significantly different to both Stalker and Roadside Picnic. The anomalies and artifacts are clearly inspired by RP but the journey doesn't involve companions, a bar/black market, any reference to life outside the zone or a clear wish granting role [spoiler]even if it does play that at the end[/spoiler]. The radius itself has more in common with the zone in RP, being [spoiler]something alien, conscious, and unearthed by man/woman's hubris[/spoiler], whereas in STALKER the noosphere was a natural phenomenon prior to the experiments that created the zone.

There seem to be some differences between 1.0 and 2.0 regarding the ending. I think it was implied in the fomer that [spoiler]neither you nor Katya actually exist, instead being amalgamations of the memories of the people that were killed/absorbed by the radius and there's still mention of this in the game, possibly as a red herring[/spoiler]. But in 2.0 it's also hinted by Katya that she [spoiler]had a role in actually unleashing the radius after the meteorite was found[/spoiler] and is likely [spoiler]trapped until we free or kill her[/spoiler]. By the ending [spoiler]we had turned into a monster like all previous explorers as if you kill yourself you hear the mimic death scream[/spoiler] and regardless of which option we choose no real closure is given regarding the fate of the radius itself.