The DJIA is not a single "thing" that is subject to the same growth rules as a single organization -- it is just an index of companies. The same properties that allowed the index to grow from 66 to ~11,000 in the 20th century could just as easily allow it to grow by a similar percentage in the 21st century: the absolute value of the index is not relevant (it already accounts for stock splits).
Well, all "things" are made up of smaller "things"... Because the DJ is made up of smaller things, it's not subject to any growth rules? I'm not sure why you'd draw a line there.
The question that Buffett is addressing is, "Is there as much potential for growth among these companies (and the economy as a whole) as there was 100 years ago?" His answer is no. While I'm not convinced, I don't think it's a "dumb" conclusion.
I didn't say it was a dumb conclusion, but just that the particular argument made to support it was dumb.
In particular, I qualified with Now there may be reasons not to expect similar returns in this century as compared to the last, but this is certainly not one of them. and This is not a discussion about whether we are actually in for similar, higher, or lower returns.
There may well be reason to conclude that there is less potential for growth -- the problem is that his reasoning for making that conclusion is based on the absolute value of the Dow index, which is what is dumb.
