Sure, but being stable doesn't mean being frozen. A steady uptrend is more desirable than these bumps. Have it at 5 and 2 months later at 7, 2 months later 9, etc, is normal and good, but have it going up 100%+ in one month, knowing it will be "corrected" shortly after, isn't. Merchants may be now selling their wares for 10 BTC (130 USD) and restock next month with BTC @, let's say, 7 or 8 USD, so they've sold that for only 70 or 80 USD, and this is a problem, unless they run to exchange it to fiat, but then we will never have a bitcoin economy but a "bitcoin paypal" instead.
Any merchant who doesn't update their prices more than once a month probably shouldn't be a merchant ... for a lot of reasons.
It is pretty easy for a merchant to support dynamic prices in BTC so they get the same amount of fiat currency to rebuy inventory. Hell bitpay is even clever enough to allow a merchant to take 85% in fiat and 15% in BTC so they can pay the bills and still have some long exposure to bitcoin.