Your point is well-taken. But it appears from Irenaeus's writings that by "tradition" he meant those things that originate with the apostles in the Scriptures, that were subsequently preserved by the presbyters. I believe that Irenaeus would say that Scripture is superior to tradition, and that any tradition that is not founded in Scripture is no tradition at all. However he does not appear to have a consistent definition for the word: "tradition". He appears to assume that what his church at that time believes and teaches is a traditional and in line with Scripture when some of it clearly is not.
Well, so says Uncle Chip, but I'm not sure Uncle Chip can necessarily make that determination any more than I can! :)
We have a tendency to look at the early Church with certain assumptions about what it *must* have been like (based on our own interpretations of Scripture), rather than looking at it for what it actually was. Clearly, Irenaeus thought that what he was saying was right in line with what the Apostles taught. I'm not sure we're in a great position to contest him on that point...especially since we don't find his contemporaries writing tracts saying that he was dead wrong.