How do you explain that pretty much every computer can print to pretty much any printer even if it doesn't recognize it? Basic, common, print drivers, perhaps? Sure, you can't take advantage of every whiz-bang feature a particular printer offers without its own special drivers, but printing a plain text document is not complicated.
And how do you explain the magic behind sticking a flash card into a printer and photos coming out? Everyone's flash card has every printers' drivers on them? No. Printers already know how to print common things. They know it innately.
Any computer can print to any printer without recognizing it? Not for anything more complicated than plain text.
For real printing, though higher end laser printers generally support PostScript or PCL language standards, inkjet printers generally do not, and require a driver be installed in order to print. Worse, many of these inkjets and lots of cheaper laser printers are host-based printers, which are essentially dumb machines that require the print job to be rasterized on the host PC. There are tons of different print engines (and variations within engines) used on such printers, and Apple certainly has no reason to try to create printer drivers for every consumer inkjet released in the last 10 years. As for printer manufacturers, while they might create the necessary drivers for some of their printers currently on the market, you can bet they'll ignore all older devices (most ignore older machines even on new desktop OS releases), as well as the lower end models in their current line-up.
Also, given iOS devices' limited resources, rasterizing a print job on the device (which is required for these host-based printers) would be slow and a massive memory drain -- and would have required a HUGE amount of work on Apple's part to even allow for such background printing applications to be used.
As for printers being able to print a file directly, that is handled completely differently than printing from a PC (or potentially iOS device).
It really shouldn't be that hard for an iOS device to send basic print requests to any printer. It might not support quality levels, front+back prints, collation options or all that jazz.. but that's probably not what most people want to print. Home users that I know print: plain text emails, coupon images, resumes, school papers, and maps.
This is exactly how Apple should have solved this. The storage space on Apple's side is irrelevant because they've already allocated that space to hold those drivers for Mac OS. And most printer drivers I've ever seen fit easily enough on a floppy disk. That's a tiny amount of space relative to any iOS device's capacity. And downloading would rarely be a problem; the iOS device either has 3G built-in, or chances are, the wifi network it's using to access the printer it's trying to print to also provides internet.
That's why it was always so absurd that iOS never supported printing in the first place. They have the infrastructure to solve the problem seemlessly and easily. The solution isn't challenging. The only explanation is that there must be some underhanded licensing fee to be an Apple-ready printer or something else entirely unrelated to actually printing. Or Apple is pushing their own printing standard agenda or something.
Your solution to making print drivers available is simple enough, but, again, there's no such thing as a small number of generic print drivers that would work across nearly all printers in the marketplace. Also, printer drivers fitting on a floppy disk is definitely not the case with print drivers for host-based printers when used on non-Windows operating systems. Since those printers are really designed to interface with Windows GDI system, using them on alternative OS's requires MUCH larger print drivers. HP's basic Linux print driver for their current Inkjet printers (no scanning, no add-on crapware, etc) runs over 20MB. The print drivers for HP and Epson printers that ship with Snow Leopard come in at 366MB and 288MB respectively, and there still isn't support for all models. That would be fun to deal with on your phone/tablet. They certainly could allow PostScript and PCL printing only, but then you (and everyone else here) would be upset instead that they had to buy a new laser printer in order to print from their iOS device.