that's part of it, but not nearly as large a part as you'd imagine. there are ways to defend against, e.g., someone getting the X both ways on a triple letter score (the most common large "tile lottery" moment). harder to overcome is someone simply drawing one bingo after another (possibly by being lucky with the blanks and Ss), getting an early 100-200 point lead, and then simply closing the board down (both players have low-scoring moves thereafter, but you already have the lead), or having a close-fought game be irretrievably lost because you get a final rack with six vowels, or none, or an unplayable Q that hits you with a 20 point penalty and let's your opponent play his final rack out letter by letter, for a large number of points.