Of all the things that investors need to be worried about heading into Apple's (Nasdaq: AAPL) quarterly report on Tuesday, the last thing that they need to be losing any sleep over is the tech giant's iPod business.

"No kidding, Rick," you spit back at your monitor -- but that mindset apparently isn't universal.

Fortune's Philip Elmer-DeWitt appeared to be in worrywart mode on Friday, compiling all of the major analyst projections in his usually insightful "Apple 2.0" column.

Gathering 43 analysts' unit-sale estimates, he finds that the consensus points to an average 7.2% year-over-year decline in the number of iPods sold this past quarter.

This would be problematic if this was, say, 2004, but it's immaterial now. For those still unconvinced of the triviality of this particular metric, let's go over a few of the reasons this doesn't matter.

1. It's all about the iOS, baby
Elmer-DeWitt points out that iPod sales peaked when Apple sold 22.7 million iPods during the 2008 holiday quarter. Have you noticed sluggish financial performance at Apple over the past three years? Of course not. The iPod's slow fade has been more than offset by the rapid ascent of the iPhone and iPad.

Isn't an iPhone an iPod touch that makes calls? Isn't an iPad a super-sized iPod touch? All three devices run on Apple's proprietary iOS, and this is the only growth that matters. In fact, it should be fairly obvious that selling pricier iPads and contract-tethered iPhones is more important than the lowly iPod. This is like worrying that McDonald's is selling fewer cups of coffee now that it's moving more lucrative lattes, cappuccinos, and iced mochas.

Apple revealed last month that there were 200 million iOS devices out in the wild, a figure that's doubled over the past year. It's the growth that matters in the App Store world we live in these days.

2. Smartphones are Swiss army knvies
It's not just handheld media players that the iPhone in particular and smartphones in general are replacing. Why do you think Cisco (Nasdaq: CSCO) shut down its Flip camcorder line three months ago, and image-sensor specialist OmniVision (Nasdaq: OVTI) moves more on smartphones than digital cameras these days? As smartphones and even feature phones roll out with better-quality cameras, there's less of a reason to carry around a standalone unit.

Handsets from Apple and those fueled by Google's Android have been on fire since around the time that iPod sales peaked. Yet even so, the iPod remains the undisputed champ among portable media players. It's holding up better than its competition.

The second leading maker is SanDisk (Nasdaq: SNDK), the flash-memory giant that's expected to post a dip in year-over-year profitability later this week. Microsoft's (Nasdaq: MSFT) virtually discontinued Zune runs a distant third.

3. See you on the bottom line
Even if the iPod were still relevant, and not the transitory technology that it's become, Apple's earnings growth would be the ultimate vindicator.

Analysts see Apple's profitability growing 65% to $5.80 a share in its latest quarter, a figure that, I should add, continues to inch higher with every passing week. It also bears pointing out that Apple has routinely smashed through Wall Street's income targets with ease over the past few years.

These are the same analysts who, on average, see iPod unit sales taking another hit this quarter. They're baking these metrics into modeling Apple's profitability, and they still see a company that's growing considerably faster than its cheap earnings multiple in the teens.

In short, don't fret the iPod's decline. Celebrate it!

Disagree with Rick? Do you think the iPod is still a needle mover for Apple? Share your thoughts in the comments box below.

The Motley Fool owns shares of Google, Microsoft, Cisco, and Apple and has created a bull call spread position on Cisco. Motley Fool newsletter services have recommended buying shares of Cisco, Apple, Microsoft, and Google and creating a bull call spread position in Apple. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.

Longtime Fool contributor Rick Munarriz is starting to see more Apple products creep into his home lately. He owns no shares in any of the companies in this story and is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.