Yes there could be a psychological element. Some alcoholic drinks are an acquired taste, so maybe the "improvement" is just the process of acquiring the taste over the first half dozen or so drinks.
However, there is a definite process of improvement in bottle conditioned beers, particularly lagers. I keep tasting notes and have brewed many beers that I described as bland/sulphur/cloying/flat/insipid/hazy/bitter/vegetal etc at first pour but revise to perfect/delicious etc. as much as 3 or 4 months later after cold storage. I know for sure that storage improves clarity, carbonation, attenuation and smoothness, but I think there are chemical processes at work too, such as fusel alcohols reacting with acids to form flavor esters.
That said, I've no doubt you can shortcut the lagering process by kegging and that's the best way to package beers flavoured primarily by aroma hops. With kegged beers there's a higher risk of oxidation as there's no secondary fermentation to scavenge oxygen, so brewers who keg naturally find that fresh is best.