The Game Boy Color had shipments in the US of 

8.7 mill (FYE Mar 2000)

7.74 mill (FYE Mar 2001)

Then the GBA simply picks up right where the GBC left off in its first two years:

7.5 mill (FYE Mar 2002)

7.8 mill (FYE Mar 2003)

Nintendo's shipment data is for "the Americas," which includes all of North and South America, not just the U.S. There is NPD data for actual sales for just the U.S. for handhelds going at least as far back as 1995.

Shrugs. Seems fairly consistent to me. Once Pokemon took like crazy around late 1999 in the US, Game Boy brand sales in the US were high, that wasn't an "unexplained" anamoly though. 

The DS was the anamoly in that it had a slow first two years in the US, but even then Nintendo quickly returns to 7+ mill handheld sales in the North American market fairly quickly and then of course begins to crush that number. 

Nowadays, 3DS is going to probably have issues hitting 7 mill+ worldwide this year, let alone being to do that just in the American market like the GBC, GBA, and DS all did several times. 

3DS' peak year in the US market for sales was 4.6 million. GBC is 8.7 million, GBA is 9.45 million, DS is 12.29 mill. 3DS is odd man out there, not the GBA.

I still don't think we're on the same page here. The GBA wasn't necessarily the odd man out, but the U.S. was. Nintendo handheld sales in the U.S. (and the Americas in general) grew at a much faster rate than in the rest of the world. Again, variations in regional performance can have a huge effect on global sales. The massive spike in handheld sales in the U.S. (and the Americas more broadly) beginning with the GBC and carrying on to the GBA had the effect of inflating GBA sales being inflated in the region relative to other regions. Again, had the U.S. behaved more like the rest of the world in handheld buying habits in the early 2000s the GBA would only have sold around 60-65 million globally. The spikes caused by the GBC were more modest outside the Americas, and the GBA was not able to ride that wave of momentum like it did in America. Let's look at the Game Boy to GBA sales ratio by region:

NA: 1.07 to 1
Japan: 1.91 to 1
Europe: 1.88 to 1

Pretty much what we see in the graphs I posted last night. Now let's look at the regional GBA to DS sales ratios:

NA: 0.7 to 1
Japan: 0.51 to 1
Europe: 0.39 to 1

So, even relative to the mighty DS, which did strongly everywhere, the GBA has a relatively much greater performance in the U.S. than elsewhere. It is painfully obvious that handheld sales in the U.S. were anomalously high back in the GBA era when compared to the rest of the world. Again, the U.S. share of GBA sales was greater than its share of any other system besides the Xbox brand.

Regional variations matter. Outside the U.S. the 3DS is performing as well as the GBA. The U.S. is the odd duck here, not any one platform.  If you can't acknowledge the importance of regional differences in buying patterns (which also negates your iPad argument) then there's no reason to continue this discussion.