Well...
As a general fule for all GMs, it should be assumed that any action that an actual average human can do in real life, an RPG persona can likewise do. As very younf chiuldren have the ability to roll on the ground, a D&D character can assuredly do the same...even if in full plate armor, although there would be a good deal of effort required and theroll would be ponderous save when on a declining surface.
As for skills, that sort of a system is in my critical design view superior to the plain dlass-based game. However, if the skill-based system is very specific, it does tend to end innovation and creative thinking in favor of reliance on a dice roll. Feats are strictly for a comic book superhero game IMO, anthough special abilities of minor sort are a fine addition to the scope of character definition.
All of the above is well set forth in my
Lejendary Adventure game, BTW
Cheers,
Gary