right now anyone can get 50BTC for free (well not including electricity) but as soon as the number of ppl using it as currency increases from X to 100000X, 50BTC will have the same value as, let say 1mln $.
The reason this isn't really a financial pyramid is that the foundations of the concept of Bitcoins are pretty solid and based upon scarcity. By definition a single Bitcoin is a rare item that is uniquely identified (it comes from a specific block number generated by a specific user and can only be owned by a single person).
I should also note that not everybody or anybody can get 50 BTC "for free". All that is happening right now is a very steady and controlled process where bitcoins are gradually being added to the system. Satoshi could have been in the situation where he and he only controlled all 21 million bitcoins and then handed them out to others freely to conduct transactions. Perhaps that might have been a better way to start out as well, but it would have concentrated a whole bunch of the wealth in the hands of just a few people. What the current mining activity does is both give an incentive to be active in the protection of the network and provides a currency distribution model that places more coins into the hands of more people. Those people who are currently running miners are essentially playing a lottery game to try and win additional bitcoins where they are entering thousands of "tickets" (called "hashes" by miners) to see if they can possibly "win" the next group of 50 BTC that will be generated with the next block.
I've been successful at winning a block of 50 bitcoins exactly once, and I consider myself to have been very lucky to have done that.
I consider it wrong to even think of bitcoins to be a form of electricity but rather than a bitcoin simply is a unit of luck. You can "buy" that luck or simply have the universe align itself to give you that luck. What it means to have luck turn out to be a quantifiable value can have some profound philosophical questions if you really think about it.