For Apple (AAPL -1.00%) investors, the last few quarters have centered on the company's performance in China. That makes sense, as Apple has reported two consecutive quarters of 70%-plus year-over-year top-line growth in the Middle Kingdom, while its overall revenue rise has respectively been 30% and 27% over the last two fiscal quarters. With the company's growth in China outpacing overall growth by more than double, you can understand the interest placed on this operating segment. Below is a visual of Apple's growth in China.

Source: Apple's 10-Qs. Revenue figures in millions.

But that doesn't mean Apple's home market, the Americas, is any less important to the company. Although greater China's tremendous growth catapulted the operating segment above Europe to be Apple's No. 2 revenue producer last quarter, China still trails the Americas as far as Apple's top line is concerned. And for a mostly developed market, the Americas is still growing briskly with 23% year-over-year growth in Apple's first fiscal quarter and 19% in the recently reported second fiscal quarter.

The crown jewel of the Americas segment is the U.S. market. And the newest data from research firm comScore confirm Apple is growing its installed base at the expense of other vendors.

comScore points to a growing luxury market
For the three months ending March 2015, Apple continued to dominate the U.S. market by claiming 42.6% of the smartphone subscriber base by OEM. Apple actually grew its subscriber percentage by 1 percentage point from the previous three-month period as the company's iPhone 6 and iPhone 6 Plus paid ongoing dividends for investors.

More recently, Apple has made a concerted effort to poach Android users, and this appears to be impacting luxury smartphone vendor Samsung. Samsung's installed base percentage dropped by 1.4 percentage points, from 29.7% in the December-ended quarter to 28.3% in the March-ended one, according to comScore. For a visual representation of the data, see the table below.

Total SubscribersMar '14Dec '14Mar '15Growth, YoY*Growth, Sequential*
Apple 41.4% 41.6% 42.6% 1.2 1
Samsung 27% 29.7% 28.3% 1.3 (1.4)
LG 6.7% 8% 8.4% 1.7 0.4
Motorola 6.4% 5.2% 5% (1.4) (0.2)
HTC 5.4% 3.7% 3.8% (1.6) 0.1

Source: comScore. *percentage point.

As you can see, Apple and LG were the only vendors to register growth on both a year-over-year and sequential basis. It's important to note comScore measures installed bases within a given time frame -- not unit shipments within a given time frame -- which is a less volatile measurement as installed bases are slower to change.

Android continues its U.S. operating system winning streak
On an operating-system level, Android maintained its U.S. winning streak by claiming nearly 52.4% of total U.S. smartphone subscribers in the most recent quarter measured by comScore. Through its disparate vendors, including No. 2 vendor Samsung, the operating system remains the dominant OS. But its lead slipped on a sequential basis, dropping from 53.1% in the December-ended quarter as more Android defectors upgraded to Apple's newest iPhone iterations.

As Apple is the only vendor to use iOS, its OS numbers during that time frame matched its vendor numbers, rising from 41.6% to 42.6%. iOS was the only operating system to grow its installed base over the three months, as Microsoft Windows Phone OS and BlackBerry lost market share and open-source Symbian still barely registers as an OS in the United States.

For Apple investors, although China is currently the most exciting operating segment, it's good to see the company is continuing to execute here in the United States.