Yeah, but if you are primarily wondering where to put your money, it is relevant! If it's "Invest in Amazon" vs. "Invest in Amazon competitor", Amazon outperforming the competitor is much more important than Amazon's absolute performance.
Most investors, however, can put their money into BP, GS or GM if AMZN and all it's competitors are tanking.
As an aside, I think looking into mining, deep water drilling, pipeline and transportation stocks would be more lucrative. As an amateur investor, I put my money where my mouth is this summer:
TCK, SWC, KMP, SDRL, HERO, CJES, JBHT, XPO
On the risky consumer side:
GDOT, LEAP
I think in Apple's case, strength relative to competition is a little redundant because if you're buying an Android tablet, then you're generally not buying a Apple tablet.
In Amazon's case, on the other hand, a lot of people consider their competition to be Walmart. Still, I (and many other consumers) shop from both places simultaneously.
Amazon can get stronger without Walmart getting weaker; I wouldn't really say the same about Apple and Apple's competition.
This article is generally good, but this bit is wrong. The markets believe Amazon will be in a stronger position in 12-24 months. Relative to competitors is mostly irrelevant - if Amazon is the last man standing, but has shrunk 50%, you still lost 50%. Similarly, if amazon grows 100% but it's competitor grows 200%, you still doubled your money.
(The only place where "relative to competitors" matters is if you have some reason to throw a fixed amount of money into a sector, but you are free to pick the best of the sector.)