The “element of chance” in roulette is where the ball lands. Thorp and Shannon did not alter this in any way.
They predicted where the ball would land. This is something most gamblers try to do, and which the casino encourages them to do, with displays of which numbers are “hot” or “cold” or the like. The only difference is that they were successful while others were deluded. This does not make them cheaters.
In your followup you fixate on the notion that they had information which others at the table did not. This is not cheating, as established by Nevada case law. If the dealer at blackjack deals cards in such a way that a skilled observer at one position on the table can see his hole card, but others at the table cannot, the courts have ruled that using that information is not cheating.
As for your example of marking cards at poker, the crime there is in marking the cards, not in observing marks that may already exist. Thorp and Shannon did not tamper with the roulette equipment in any way.
…and anyway, even if you find all those arguments unconvincing, ask yourself this:
If using a roulette computer were cheating, then why did Nevada bother to amend their laws in 1985 to add the device statute? And why were the many people openly advertising blackjack computers for sale before 1985, under their own names, never prosecuted for possessing and selling equipment intended for cheating casinos? Obviously, it’s because everyone involved knew that the laws regarding cheating didn’t apply, and they needed something new.
