Repeating....There is no serial COM port header on the P8P67 Deluxe. I'm sure of that. You're guessing.
It's user ignorance that allows Asus to get away with crap like this. No doubt you also consider the matter trivial as they obviously do.
OK, time to stop guessing. The P8P67 WS Revolution definitely does and so does the P8P67 Vanilla Rev 3.0 does. I'm fairly certain the P8P67 Pro has it as well. And actually I have seen the P8P67 Deluxe. I reviewed it in fact. It's been awhile and I didn't remember whether it had that port or not. I tend not to pay too much attention to COM ports because most people don't give a shit about them. The P8P67 Deluxe I reviewed didn't have it now that I'm looking at the pictures. Why all the others have it and the Deluxe doesn't, I can't say. No clue on that one. Still, who cares? How many people actually use that feature? And yes, I'd say it's pretty trivial. The BIOS / UEFI for each of these boards is pretty much identical which makes things easier for them. Most people don't use the COM port and even fewer care about the resources it may grab. If you don't like it, you can simply disable it and recover those few resources it does take. It would have been nice for ASUS to have spent more time on customizing the BIOS for the Deluxe, or making it so you could actually use that port like they did with all the other boards in the series, but again it's not a big deal.
As for the comments about the firmware being behind on the ASUS, I'd disagree. How many of you have worked with Gigabyte, MSI, Intel, and other brands of boards recently? MSI's Click BIOS is terrible and Gigabyte is using the tired old BIOS interface. Intel is using UEFI without the menus and a horrid BIOS layout. ASUS has flaws in some of their designs and UEFI implementations but they are setting the bar. Everyone else is playing catch up to them on the BIOS / UEFI front.