Meantime, it wasn't all that surprising to see Apple ( AAPL) shares shrug off a rare downgrade on Monday, but it was worth noting that the call made by BTIG Research is really looking further out, raising questions about whether the company's iPhone business could be hurt by wireless companies pushing back on subsidizing upgrades as 2012 progresses. The firm argues that AT&T ( T), Apple's biggest customer, and the other wireless providers have to take this step to protect margins and theorizes a repeat of Apple's one hiccup last year could be in the offing. "We expect quarterly upgrade rates to contract further in calendar Q2 (Apple's Fiscal Q3) based on typical wireless seasonal trends and likely increased speculation on the anticipation of a new iPhone in the second half of the year," wrote BTIG analyst Walter Piecyk. "Recall that investors were surprised by Apple's Fiscal Q3 results last year because of the slowdown in iPhone sales ahead of the expected launch of the iPhone 4S. We also do not expect a material broadening of market launches for the product like what was seen in the first calendar quarter." It's difficult to overstate Apple's importance to the broad market at this point. For example, the blended earnings growth rate for the S&P 500 currently sits at just 3.2% for the first quarter, according to Thomson Reuters, but that estimate drops down to 1.8% if Apple is removed from the equation. As for Tuesday's scheduled news, Alcoa ( AA) is the big name on the earnings docket Tuesday. The aluminum producer is traditionally the first Dow component to report its results each quarter, and it's slated to reveal how it fared in the first three months of 2012 after Tuesday's closing bell. The average estimate of analysts polled by Thomson Reuters is for a loss of 4 cents a share in the first quarter on revenue of $5.77 billion. An in-line performance would represent the company's second straight quarter in the red as Alcoa struggles with lower pricing and the impact of Europe's sovereign debt woes on demand.