I agree! Gambling becomes a problem not just when money is lost, but when it starts hurting your life, affecting your daily routine in other ways. If it affects your health, job, or even relationships, then it's already a serious issue, even if you haven't lost much money.
It's about the impact on your life, not just your wallet.
This, amount differs to person's availability to generate income (job), state of life, etc. thus it differs the amount they bet but worst thing to happen is when gambling start to destroy your self and your life. It has many side effect just like what had you mentioned, worst is it affect your relationship to others, because if it happens, you only have you, if you don't help yourselves then it will end up getting bad.