It seems the main cryptos are divided into (very roughly) two parts: the original plain blockchain-based cryptos such as BTC, BCH, LTC... on one hand, and ethereum on the other hand which allows the deployment of smart contracts. At first, I thought ETH was the currency used by these smart contracts on the ethereum network, but then I saw that each company willing to run on ethereum (OmiseGO, Golem, etc.) issue their own tokens that should be used to pay for their services.
Sure, those tokens can be bought using ETH, but they can also be bought using e.g. BTC, so it seems one could just use smart contracts/dApps, BTC and tokens, and never has to use any ETH. Am I missing something and does ETH plays some special role?
(Please note my question is not about transaction fees nor velocity. I am not trying to advocate using BTC: it just happens to be very widely used on exchanges.)