Back in 1998 Apple removed the floppy from the iMac G3. There is no argument that it was obsolete technology. Small, easily damaged with better replacements like the zip drive, cd-r, usb sticks, and networking. For those who still had floppy disks you could get a usb drive. The iMac G3 led the way and the rest of Apple products followed suit.
One of the primary data replacements of floppy was the "cd". The cd drive, cd burner, dvd drive, and finally dvd burner while useful is less useful than it used to be. Most backups don't fit on dvd drive. Software and games are usually downloaded and not bought in a package these days. CD's are no longer bought and ripped, but usually obtained also online. Even movies are transitioning to streaming services. Even creating home dvd movies has been depreciated in favor of posting online. The big final reason was the OS install disk, but that is now just a usb stick. Just how back in 1998 we still had a pack of floppies disks on the shelf we have dvd's lying around. But we can get one external drive to share among the computers as we transition. I myself plan on pulling out mine from my MacBook Pro and putting it into an external case with a optibay. Replaced with the internet and usb sticks disk drives are dead.
As for ethernet, 802.11n is around 130Mbps (real world) which is decent for most everything. Other than transferring GB's of data WiFi is good enough. Backups are the biggest thing most users will transfer, but even that is done overnight (over WiFi!) and in the background. After the disk drive the ethernet port is pretty tall so removing it allows for thiner laptops. At the end of the day, like the floppy if you really need an ethernet port you can get a usb version and just like the Firewire port it will get the axe on MacBook models.
The last ten years the speed of the cpu on the computer has had less and less of an effect on the performance than one would think. First was the race to 4GB of memory, followed by graphics and now io speed.
The most dramatic improvement someone can make to their computer these days is to switch to a solid state hard drive. As the size of flash has continuously increased while the price has dropped it becomes more and more attractive for everyone from desktops to server farms. There is a lot of research and experimentation in this area with leaps in performance coming out all of the time. The next several years will be very interesting to watch as flash grows. While it seems mature flash is still new enough to warrant whole blog posts by users who just upgraded extending the virtues. From the lower power requirements, the lack of any noise, fitting in different shapes, and of course mind boggling speed, ssd drives are the future. Apple has offered flash as an option for a while now on some of its computers, but with the new Air it takes the option away and makes it the default. As prices continue to drop and sizes rise ssd will become less and less the option and more the default (or only) option.
It would be no surprise if in the next refresh or two the macbook moves to ssd and drops the super drive and ethernet port. The MacBook will be thiner, have a longer battery and a faster user experience.
As the tagline says:
The new MacBook Air. The next generation of MacBooks