This sounds great (and it is to an extent), but exclusively obtaining data from brick-and-mortar big box and retail stores is fatally flawed for premium level computer sales. I'm sure Apple still has an enormous market share, but it won't be anywhere near that big. The reason being that most $1000+ PCs fall into three categories that will NOT be picked up in their data:
1) Gaming PCs - Most high-end gaming desktops/laptops are purchased built-to-order online from the likes of Dell, HP, Alienware, Falcon northwest, and other many other smaller boutique vendors. You will NOT find these at a BestBuy©.
2) Ultraportable laptops - These would be laptops from Sony (TT, Z, etc) Panasonic (W5, T5, etc), Toshiba (various models), IBM (X300, X200, etc), Dell (adamo), etc. You would be hard pressed to find many at retail stores besides a few of the Sonys. Many are available online-only, and a lot of them are purchased grey-market from Asia.
3) Workstation and Workstation laptops - high-end workstation PCs from the likes of Dell (Precision), HP, Lenovo, and others are definitely not found in retail stores. They may also not be included anyways as they are seen as "business" computers, although many consumers buy them because of their quality/durability/performance.
Lastly, even regular, mainstream consumer desktops and laptops found in most retail stores and big box stores are of the budget and average variety as that is the clientele they are servicing. Rarely do you ever see $1500-$2500 PCs at a Best Buy, Frys, or Walmart.