Ted Aronson, the veteran Philadelphia money manager, just pulled up a list of the most valuable US companies (based on share price), and compares it with a list from the end of 1978, when he was a "young pup" at the vanished Philadelphia brokerage Drexel Burnham Lambert (where Aronson shared the floor with ambitious youngsters like future junk-bond king Michael Milken, and briefly bossed future Comcast chief Brian L. Roberts).

Heading the list at the end of 1978 was IBM (now #3), AT&T (now #8,  after spinning off Verizon and much more), Exxon (now #1), GM (dropped off the Top Ten), and General Electric (still #5).

Kodak and three oil companies have dropped off the list, replaced by Microsoft, Procter & Gamble, Warren Buffett's Berkshire Hathaway, and Wal-Mart. Chevron moved up the list, to #4, from tenth.

So what's changed in a generation? There's more tech stocks at the top of the list - but, as a group, Apple, IBM and Microsoft, combined, are now no bigger than IBM was, all by itself, as a percentage of the major US stocks, Aronson notes. 

Bottom line: Turnover on the Top 10 list, over 33 years, was just 50%. That's a buy-and-hold message, and a warning to amateur traders and people who think today's trend will be their friend.