As others have pointed out, it doesn't make it any less fair. It does mean you're wasting some time scratching to see numbers, or waiting for a roulette ball to land, or waiting for cards to be dealt... but that's a choice the user makes to make it more entertaining.
Personally, I love playing roulette/blackjack in a real (offline) casino - if i just walked to the front desk, handed over the amount of money I was willing to part with and asked them to randomly generate my winnings/losses, I wouldn't ever bother.
And the same applies for online - I'd be far more likely to play an online casino game as time-killing entertainment than as a way to make money.
You're wasting time in that the server could just as easily say "win" or "lose" rather than making you spend that time pretending to scratch numbers. It's no more wasteful than a paper scratch card, except that with the paper scratch card the waiting is a necessity, whereas online it is not.
That said, my use of the word "waste" is not meant to be negative - they've left that feature in the online version of scratch cards for a reason, because they feel people prefer to have that time wasted - and, as I said, if playing online roulette, I would rather waste time seeing a ball roll around than just being told if I had won or lost.