Evan Schuman's StorefrontBacktalk

Amidst all of the reports this week detailing record-breaking revenue for the start of the holiday shopping season, one critical point has been overshadowed. While E-Commerce sales have indeed been strong, the rate of increase has been essentially flat for the third year in a row. Indeed, the rate of increase of sales this year is projected to be lower than either of the other two most recent years.

EMarketer’s comparison stats only go back to 2007, showing a 19.4 growth in 2007’s holiday season, an unusual drop in 2008 (-7.8 percent) and then three similar growth stats for 2009( 16.9 percent), 2010 (17.4 percent) and 2011 (16.8 percent).

Statistics being statistics, they can mean whatever we want them to mean. On the happy side, in this economy, a steady 16-17 percent annual growth rate is pretty nice. And given the steady (other than 2008) E-Commerce revenue increases through this year’s projected $46.7 billion online holiday season, the slight drop of growth percentage is certainly acceptable.

But with the revenue hype fest that has been going on the last few days, it’s worth remembering that this year is simply projected to have the same kind of season-over-season growth that it’s enjoyed the last couple of years.

The more interesting question is the degree that these E-Commerce numbers reflect cannibalization of in-store sales. Figuring that out will get even more difficult as we expect a lot of analyst houses to try breaking out mobile (smartphone and tablet) figures next year.

There are two issues behind this. First, theoretically, a dollar in revenue should be more profitable if it’s generated online than if it happens instore. The reality is that is only true if the chain is shifting enough sales to online to justify reduction in in-store personnel and closing/shrinking stores.

The second issue is where those E-Commerce sales are coming from. Are those sales that would have otherwise happened in-store? Are they coming from sales that would have otherwise gone to rivals? And are those convenient online sales costing you millions in lost in-store impulse purchases?

EMarketer analyst Jeffrey Grau pointed out another cautionary note to this week’s exuberant numbers. Given the strength of discounting, he’s seeing evidence of consumers merely pushing a higher percentage of their overall holiday purchases in these first few days. “People are loading up early,” Grau said, which suggests the early strong numbers will be balanced out by weaker numbers for some of the season’s remaining shopping days. That’s why he’s projecting that, when all is wrapped by Dec. 25, the percent increase this year will be roughly the same as last year and the year before.

Bottom line: the E-Commerce stats are nice, but don’t get cocky.