Apple's (NASDAQ:AAPL) earnings tonight have left the company down 10% in after-hours trading. It doesn't require being a stock market genius to see that investors were disappointed with the company's results. 

Yet looking across the past quarter, one product group is the most striking: the Mac. The iPhone saw 28% more sales than the fourth quarter of last year, while the iPad achieved 22% revenue growth in that time. Those numbers stand in stark contrast to Apple's Mac lin-up, which fell a surprising 16% from a year ago. To put that in perspective, that's a steeper decline than the iPod, a product line that has long been declining. 

In the following video, Eric Bleeker and Andrew Tonner look at Apple's weak Mac sales and discuss whether the company is succumbing to the same PC challenges that have been affecting companies such as Hewlett-Packard. Previously, Apple had managed to dramatically outperform the broader PC market, but it appears the disruption it's caused in PCs is finally catching up with the company. That could cause some near-term adjustments for how Apple investors think about the company, as one Mac creates the same profit as about three iPads, but Eric also warns that if Apple's struggling in PCs, its just another warning sign how challenged the broader PC industry and its players -- such as HP, Intel, and Microsoft -- will be in the year ahead. To see their full thoughts, watch the video. 

Andrew Tonner owns shares of Apple. Eric Bleeker, CFA has no position in any stocks mentioned. The Motley Fool recommends and owns shares of 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. The Motley Fool has a disclosure policy.