I'm not sure it is period-specific. After all, the Basic Role Playing system awards experience on a per-skill basis, based on actual use and specific training, so you get better at what you actually do, regardless of whether it is combat-oriented or not.
I believe, on the other hand, that the level-based systems tend to have combat-focused experience, because they approximate experience with conflict resolution, and conflict resolution with combat. It is even more pronounced with class-based systems because an experience system must find a generic common ground between all classes, and the easiest common ground is combat.
Rolemaster starts in the category of systems most prone to using combat-focused experience. It reduces combat emphasis by adding extra rewards for a bunch of things and applying diminishing return (so chain-killing orcs loses its effectiveness over time), but still suffers from the generalisation that, since combat is available and is a challenging activity, it is still an efficient way to 'level up' if you survive the ordeal.
The amusing thing is, you could easily go towards a training-based and usage-based experience system since RM is also skill-based. It requires getting rid of development points and designing a mechanism that rewards skill training and/or skill usage in a non-routine situation with additional ranks, with built-in diminishing return (e.g. you need a number of "uses in non-routine situations" equal to X times the number of skill ranks you already possess to gain an additional skill rank, with every training period being rewarded with T uses, T being influenced by the quality of training, skill complexity and natural aptitude).
So I guess that, if RM still feels like an old-school action-rewarding RPG, it is because the class/level aspect of the system is considered more significant than the skill aspect. In other words, that players still use it as a "more realistic D&D" instead of using it as a "Runequest with character templates".