a desktop with 2x120mm fans would be a lot cooler than a tower one. right?
Please clear this points for me,
clearly, NO, a desktop with two 120MM doesn't necessarely have more airflow.
all this because hot air goes up. then, towers gets hot air easily while desktop just get any air out.
of course, two 120mm are better than one but if you take the same in a tower... as the antec P1XX series, you'll see there's effectively two 120MM on top of the case and that's why the PSU is located at the bottom of the case letting airflow go through the cpu zone.
I get the feeling that you're generalizing from an uninformed point of view. The way I see it, airflow through desktops vary widely depending on the individual model in question. And the same can be said for towers. For example, I've got a Sony Vaio mid-sized tower with lousy airflow. It has an 8cm fan on back right behind the CPU and another 8cm exhausting the power supply. That's it. When I added a second HD, the temps in the system went up above my comfort zone, so I moved the components to a Lian Li tower. It has two 8cm inlet fans blowing over the HDs, an 8cm exhausting the CPU area, the PS exhaust and an 9cm blowhole fan. The HDs run over 20C cooler in the Lian Li case and the CPU runs about 10C cooler. That's not a whole lot of fan surface area on the Lian Li but it works because it makes good use of the available draw and has the blowhole. Go do dual prime with a case that has a blowhole and try it with the blowhole functioning, then physically block it off. Bi diff.
But if you want to see airflow in a tower, look at the Cooler Master Stacker or the TT Armor equipped with the 25cm door fan and a couple of the optional iCages, which have 12cm fans on them. My Armor is set up like that, so it has a total of three 12cm fans (two inlet, one outlet), two 9cm outlet fans, one 8cm blowhole and the 25cm door fan set up as an inlet. I also use a slot fan as an outlet right above the video card and the video card is a 1900XT, which exhausts through the second GPU slot.
If you make a thorough comparison with desktops, you'll see much difference in airflow from model to model, but in general, I don't see a bunch of high airflow desktops. In the first place, many desktop cases are small with quite a bit of conjestion. The TT VF1000BWS is a decent LAN box option if you have a microATX mobo, but it has only one 9cm inlet fan and just two 6cm exhausts. You've also got the PS exhaust but the good thing is that there is a reasonably good surface are of passive vent space. The PCI card slot dummies are vented, about 1/4th of the top panel is vent, the side panels have good vents. If you use a GPU that forces air to exhaust out the back, you can run pretty cool in this case.