Wells Fargo recently downgraded AAPL stock from “outperform” to “market perform,” citing the fact that the company’s gross margins have typically fallen 2.25% in the two quarters following the launch of a brand new iPhone model (rather than an S upgrade). The company had the following to say regarding their change:

Our bullish thesis on Apple had been predicated on the expectation for gross margin (GM) expansion driven by the 5s cycle. While we still have conviction in the gross margin thesis (and the potential for iPad/iPhone unit upside), we believe this may be largely embedded into the valuation.
The bank hasn’t changed its valuation range of $536 to $581, though it’s likely expecting something toward the lower end of the range given the downgrade. Wells Fargo’s analyst Maynard Um said he believed the balance of power may be shifting away from Apple to the carriers as the carriers shift away from subsidized deals to high up-front costs and/or separate phone financing, which are in essence disguised-loans.

Source: Wells Fargo via 9to5Mac