"In another 50 years, would you expect Apple or Exxon to still be near the top of the list?". Is that a trick question? Exxon obviously - they make the thing we can't live without.
Just because people will be buying x in the future, it doesn't mean that today's top x companies will still be around in 50 years.
The computer market is now much bigger than 50 years ago, but many computer companies of that time went broke. Just like we went from mainframes to personal computers, we'll probably be using much more renewable energy in 50 years, and it's not obvious that any given existing company will adapt to it.
Also, there are mergers. Mobil and Texaco were in the top of the list in 1962, and now neither exists independently (merged into Exxon and Chevron resp.) so arguably they aren't in the list anymore.
This is hard for product and most services businesses, but in the commodities business it ought to be much more workable.