Amazon is projecting slower growth this quarter. Image source: Amazon.com.

Amazon.com (AMZN -2.56%) shares soared last week following a good earnings report where earnings per share met expectations and sales grew an impressive 24% year over year to $17.09 billion. What's particularly interesting about this enthusiasm is that Amazon's guidance for the holiday quarter was not especially strong.

Amazon projected that revenue would grow between 10% and 25% year over year in Q4. That is still incredibly strong growth in the context of the retail environment more broadly. However, the range suggests that Amazon's growth may be slower in the fourth quarter than it has been for the past six months or so.

Yet Amazon analysts do not seem to believe the company's guidance. The average estimate calls for 22.4% growth, and a few analysts are projecting that Amazon will beat the top of its revenue guidance, which is $26.5 billion. Are analysts right that Amazon is lowballing its guidance? Or are they setting investors up for disappointment in three months?

Amazon's guidance: Conservative but realistic
To better understand the nuances of Amazon's guidance, it is useful to look at how Amazon has tended to perform relative to guidance in recent quarters. Looking at Q3 specifically, analysts could be forgiven for taking Amazon's guidance with a grain of salt. It had guided for revenue in a range of $15.45 billion-$17.15 billion, and the result -- $17.09 billion -- was just below the top of that range.

However, while Amazon's forecasts do tend to be conservative, revenue often falls in the middle of the range rather than at the high end. For example, last year's Q4 guidance called for 16%-31% growth, yet revenue grew just 22%, slightly below the midpoint of the range. In Q1 of this year, revenue increased by 22% again, which was slightly above the midpoint of the 14%-26% guidance range.

In fact, prior to last week, Amazon had not come within 1% of the top of its guidance range (or beaten its sales guidance) since Q2 of 2011. This suggests that Amazon has generally provided realistic guidance. There is no reason to believe that policy has changed recently.

Holiday struggles?
I think there is a good chance that Amazon will see a repeat of last year's "holiday struggles" this quarter. Obviously, 20% sales growth in the busy holiday quarter would be unbelievably good for almost every other mass retailer on the planet, but for Amazon, it would be a disappointment.

Amazon's biggest point of differentiation for customers is low prices. The company constantly pushes to gain market share by improving its efficiency and then passing the savings along to consumers. However, while Amazon goes for bargain-basement prices all year long, most other top retailers save their biggest discounts for the holiday season.

In other words, Amazon is likely to have a smaller or non-existent price advantage during the holiday season, whereas it can often be a price leader for the rest of the year. This will have an incremental negative effect on Amazon's growth during the fourth quarter. (Another negative factor is that the fast-growing Amazon Web Services unit makes up a smaller portion of Amazon's revenue in Q4 due to the seasonal uptick in retail sales.)

Foolish wrap-up
Amazon has consistently posted revenue growth above 20% for almost its entire history -- the Great Recession is a notable outlier -- something that has endeared it to investors. However, its guidance for sales growth of 10%-25% this quarter suggests that it may fall short of this growth rate in Q4.

Amazon analysts, having seen the company maintain its 20%-plus growth rate for so many years, are discounting the possibility that Amazon is facing real headwinds this fall. If revenue growth does drop below 20%, investors are likely to be very disappointed, and the stock could give up most of the gains it has posted this year.