What matters is not only that there's a limited supply of Bitcoins, but that BTC has a network effect behind it. Almost nobody is accepting LTC, and literally nobody is accepting other currencies.
Not to mention the safety - it's easier to pull a 51% attack on the other currencies (see the attack performed on Feathercoin)
Not to mention the safety - it's easier to pull a 51% attack on the other currencies (see the attack performed on Feathercoin)