Really, syntax "nba.head(1)" is not any more "object-oriented" than "head(nba, 1)" -- it's just syntax, and the R statement is in fact an application of R's object system (there are several of them).

IMO, R's system is actually more powerful and intuitive -- e.g. it is fairly straightforward to write a generic function dosomething(x,y) that would dispatch specific code depending on classes of both x and y.