Preferential shuffle is illegal. I've seen it happen, but most casinos don't do this. Its easier to just ruin the penetration. Very, very few dealers know how to count. Surveillance people are the ones who know about that stuff.

You're right about everything else except the advantage. It is possible to gain up to 2% advantage using a sophisticated system, more in some special situations. This may not seem like much, but it is 2% compounding hourly, or something of that order. If you are playing 100 hands per hour averaging $100/per hand, you have $10,000/hour of action. 2% of that is not a "slight advantage" by any means. It is many times the advantage the house has against a perfect basic strategy player and is plenty to make a nice living, if you can find enough games.

The issue is not the small advantage (because the advantage is rather large), the issue is the variance. Variance comes from how the game is constructed and is the real reason why it is difficult to play blackjack successfully.

Many people learn a basic +/- count and think they have the advantage. Doing it correctly is much more complex.

Oh, and usually its a very pleasant woman...