as a professional enthusiast, I would have thought you would be well aware that _everything_ broadcom puts out is proprietary. So it should have been no surprise that their wifi card shipped with the mini was also going to be using a binary blob/firmware method to interface with the kernel.
Intel does the same thing. So i hope you aren't looking into buying an intel mini pcie card.
There is an open source broadcom driver bc4 or something like that. They're working on supporting the card that comes with the mini's but as far as i know, it's not working yet.
Ubuntu is in the business of making an easy to use distro. They will have non-free software included to make that possible. This includes nvidia's closed source drivers, broadcom's, intel's and anyone else (software too like macromedia's flash plugin). That's what ubuntu is. As a professional, you probably should have already been aware that ubuntu is not Debian for that reason. If you want free, you use Debian. If you dont care if it's free, you just want everything to work out of the box, that's why Ubuntu was created and tailors to.
Now, like any good distro kernel, they're going to be bloated with drivers you dont need, nor want. Options will be set to cover the widest range of hardware, not the particular subset you have. Obviously, with ubuntu, like any distro, you have the choice of simply compiling your own after installation. I highly recommend going that route if you know what you're doing.
My suggestion for the wifi is to pick up an atheros mini-pcie card that comes from other netbooks like the aspire 1 or such and use the ath5k driver. It works, it's firmware/binary blob free and you should have no problem at all with it. it may get a bit hot if you're straining it (weak signal to your ap, weak being < 40%) though.
Dell chose to go this route rather than the more dogmatic Debian (which is the best, the best there is or was or ever will be) because Debian requires a certain amount of effort from their users. While that's fine for some, the majority of Dell's customers probably would just look like a deer in headlights if they had to deal with an OS that by default didn't support all their hardware because of licensing conflicts. Ubuntu is a perfect linux fit for Dell. Why dell chose to go with a broadcom card instead of an intel or much better and completely open source supported atheros card is probably a money thing. They probably had some deal to get the cards really cheap out of the other choices. Plus, the broadcom card is probably a lower power card compared to atheros. You have to remember, most people aren't concerned with licensing terms, so that was likely never a factor in the decision making process of what hardware to use to best appeal to their customers.