To be honest that is one of the things I like from Mazda, they are a small car manufacturer so they cannot completely reshape models every 2-3 years or so, so if you buy a car you really like then it stays pretty much the same (yeah yeah some facelifts but that's it) for several years, just look at the Mazda3 (2004-2009) and the Mazda6 (2003-2008) and still beat competitors in many areas.
One of the cool things Mazda has done is recent years is make little changes. take the ever-changing grille on the Mazda3 for example. The body essentially stayed the same, but the grill has a few different iterations. also, Mazda has been pretty good about changing wheel styles with the "face lifts".
Another thing that I find interesting is that the 5 is selling so well, but most that I see are at least mid-line touring models. There are Sports like mine out there, but people seem to want to pay for the slightly higher end models. I notice the same across the Mazda lineup. If you are selling models with more content, you don't have to sell in volume to make money.
On the flip side, Mazda has standardized so many components across trim levels then even the base models are pretty feature rich. Economies of scale dictate that all of the cross-component sharing means that prices go down even though the content level has gone up. It also meas that the most basic Mazdas all still have that awesome Independent suspension setup. In fact, my understanding is that Mazda basically doesn't have sport suspensions on the 3 5 and 6, just bigger wheels and/or brakes.
I think Mazda has a great strategy, especially for a smaller market share automaker. They don't really compete on the low end, but do price out well when you get the feature that people really want in a vehicle. And when there is enough demand for say larger wheels and leather wrapped steering wheel, but no desire for say a sunroof or 6 disc changer, viola, the Mazda 3 VE (value edition). The parts are already bought for higher trim levels and maybe there are some extras sitting around anyway, so the cost to manufacture isn't that much higher than a standard 3, so the price can stay about the same.
the other quirk that comes with parts sharing is the familiarity that shows up across all lines. I had to drive a 3 while the 5 was in the shop and had no trouble getting acquainted to it. Most of the components aren't just kind of the same, they were the exact same parts! I have also driven 3s, 6s and the 5, all with the 2.3L engine and it also has a similar character, though each model is distinct in performance. Now if they can just hurry up and the the Mazda2 4-door hatch over here in the 'States.... (don't even need a Mazdaspeed version)
