But technically it is possible, right? So what happens, when somebody smart enough will make some improvements of his own to the algorithm of adress generation in some services, like blockchain.info or others? He will gain access to your coins? Is this real?
No? Those addresses are randomly generated. It's possible to get the same address, but I don't think you can "make your own algorithm" to generate the private keys more easily.
Maybe if the service isn't pure RNG when generating those private keys.