I think that roleplaying can perhaps be defined as actions that a player character takes in an adventure. For example, a player who has a character charge a hated enemy -- either silently or with the character throwing out invectives questioning the foe's courage and parentage --- may be roleplaying as much as a character who silently and carefully moves behind a tree to get a position for a perfect shot.
A lot of roleplaying actions in a game depend a lot on the character, the player and the world. So, I think that a barbarian who boldly attacks foes can use some good judgement on tactics --- something that he may have some experience with --- but that it is perhaps fine for a DM to ask why a character is trying something unusual. (At one game, a DM grumbled about 5th level characters --- including a cleric, a wizard, and a rogue --- thinking tactically. Considering that the characters had probably fought dozens of skirmishes, and are trying to stay alive, it made sense to me for the characters to be able to discuss their actions beforehand and come up with a fairly decent plan.)
Overall, I liked Wolfgang Baur's article. I think that we may have different defintions of roleplaying, but I think that Baur makes several good points. The posters here also make good points. Perhaps one thing that DMs can do is to decide what constitutes common knowledge for characters, depending on their backgrounds and their places of origin. So, if trolls are a somewhat common threat, a PC may have a good reason to remember the stories of people using fire agains trolls. However, a PC from a region where trolls are largely unheard of might be reasonably asked to make a knowledge roll. (If the party is likely to face trolls, perhaps the first PC can share his knowledge with other PCs in a roleplaying encounter involving other party members.)
Perhaps players and DMs can work together to help establish what is common knowledge in a campaign. One way to do this is perhaps compile a list of things that all characters in a campaign are likely to know (perhaps information on common races or threats, or cultural and religious history --- a character might be able to identify a common religious symbol in their culture or the flag of the county in the country that they live in), things that are perhaps less common (knowing the flag of a distant land, or identifying the symbol of a religion largely unknown to the character's place of origin), and things that relatively few people are likely to know (the full powers of an uincommon monster, the details of politics in a land that is almost a legend) and things that practically no one knows (the greeting rituals of a secretive cult, the childhood nickname of a powerful enemy, the existence of a hidden refuge like Shangri-La.) Possiby, this could change for each character with time and experience. (For example, if the party interacts with a merchant caravan from a distant land, the party could interact with the caravan and learn a little bit about the land, the nation's history, and its flag.) I understand that the Player's Guide to the Eberron Campaign Setting has something called "The Five Things that EVERYONE in Khorvaire knows."
So, perhaps by setting up some parameters for what characters may know, based on their origins and prior experiences, it might make it easier for DMs to establish some of the feel of the setting. So, a barbarian might know that a troll might be able to reach him if he charges him could be appropriate for that character --- based on the character's background. The barbarian's new acquaintance, a wizard from a land without trolls, might have little knowledge of the monsters and little ideas of how to specifically fight a troll. (He may have enough sense and knowledge to realize that rushing up to something with long arms might be a little dangerous.) Just a few thoughts.
