Drakulie, I am very skeptical if you are saying the pros you have strung for are stringing the mains and crosses the same tension even if they are using a hybrid. I have seen numerous web pages and threads on this board showing a great deal of variety in string tensions between mains and crosses. There is plenty of information showing Roger Federer's tensions.
Tim Straw just had an article in, I believe, RSI magazine in which he states you should string poly 20lbs below the tension you were used to stringing your multi. He says it twice for impact. I think 20lbs is a little much but it does lead to questions as to what tensions to use in a hybrid string job. If you strung you multi over the years at 60lbs and now decide you are going to try a poly/multi hybrid, are you going to string the poly in the mains at 40lbs (as Tim suggests) and the multi at 60lbs like normal. I don't think so but you are not going to string them both at 60lbs as you suggest.
There are many reasons why people use different tensions between mains and crosses. They do it for spin, feel, not to distort the racquet, power, control and so on.