To my mind, the word "convention" refers to a shared practice adopted to serve some perceived practical purpose that continues (at least arguably) to serve such a purpose today, whereas a "tradition" refers to a shared practice that need not have any other justification for its continuing existence that that we or our predecessors did it in the past.
I would use the term "convention" rather than "tradition" to describe usage rules such as the one against using a comma to separate independent clauses that are not connected by conjunctions. Likewise, putting a period rather than a comma at the end of a declarative sentence is a convention, and so is using single or double quotation marks rather than commas to indicate a "words used as word." It is certainly possible to replace all of the conventional punctuation marks in the paragraph I am now writing with commas—treating them as, in effect, a unitary way to convey the idea, "a punctuation mark of some kind goes here"—and still have a consistent graphical representation of a grammatical utterance. Looking at it, however, you can see why writers and readers might find conventions that entail the use of punctuation marks besides commas (in addition to the convention of using capitalization to indicate the beginning of a new sentence) for particular purposes to be quite valuable:
