It is very common to see "you win some, you lose some." The reason why this is used in the simple present tense instead of the simple past tense is because it is a factual or general statement. Just like "grapes are good for health" or "life is not always fair." I hope this helps!

Both are correct depending on the circumstance, and both are used. That said, "You win" is far more limited in how it can be used than "You won". The difference is in the verb tense. "You win" can only be used at the moment victory is declared, as it is present tense. "You won" is past tense, and can be used at any time after victory is obtained, including immediately.