Right now XBT is skyrocketing. Looking at the ETH/BTC pair, it seems Ether is heading back towards it's base.
https://www.coinigy.com/s/i/598547f4b8fec/
But on ETH/USD, it hasn't even budged.
https://www.coinigy.com/s/i/59854849ecc5a/
Would you buy into the ETH/BTC if the base cracked, knowing it's stable against the USD?
YES YES YES and more YES. To illustrate, check the price of XBT at .0729130 at that time was roughly equivalent in USD to the price at ETH/USD. In fact at this moment you get almost $1 USD extra equity from trading ETH/XBT over ETH/USD. When trading currency pairs the proportions may look different visually due to the economies of scale.