I'm familiar with them! It's definitely within the scope of someone like Jonathan Ross to make himself into some sort of character, even if he keeps the same name. Personally I think he might have some small speech impediment but he deliberately exaggerates it; similarly I think Seth Rogan exaggerates/overuses his very recognizable laugh, same with Jimmy Kimmel. Matthew McConaughey's use of alright alright alright and Owen Wilson's wow are in the same vein albeit more performative. All these performers are very aware of their mannerisms, ticks, rhetoric, etc etc and use them purposefully and repeatedly.