Inversely, The white Macbook has an optical drive yet it's not a Pro. All I'm saying is that there's really not much meaning with the "Pro" in Macbook Pro.
But the optical drive is about the only common element, and not the differentiation. It is the difference in processor speed, graphics, ram, HD size, body and many more that make the Mac Book not a Pro. To remove the optical drive is to take out a truly standard feature in 95% of all computers sold. And yes, I've heard the "but we said the same thing with removal of the floppy". But that was because it was replaced with a much higher capacity, better physical media. USB is good, but is not able to affordably replace a 8.5 GB DL DVD that I can get in bulk for 20 cents. And can't touch a 50 GB blu-ray (which Apple is the sole abstainer from). I have Adobe CS5 Design. Downloading that is still not a realistic option for most ISPs (not without doing it over-night), and that would be a lot of USB drives, or one expensive one. And some of the files I created, I am not going to share via email, ISP's are not anywhere near that yet for upload, nor is Mobile BB. You could use an entire year's upload with AT&T with just a few files
Casual users may be able to get by without the Optical, but to me, a "Pro" capability means being able to easily use pro software, author and distribute massive files to co-workers etc. And at times, Optical media is still hard to beat for affordability and capacity. (I recognize I don't set the "casual user" definition- so just an opinion)
In my opinion, a Pro laptop is going to be normally plugged in at a job-site anyway. Sure, you want the ability to work unplugged TOO, but I view that as the Air's position. Ultra-portable, ultra-light and long battery life gained through trade-offs such as no optical, SSD etc. But I don't imagine a lot of people spending the whole day at a desk using an 11 or 13 inch air as their regular "work computer" that is plugged in at home and plugged in at work, with a larger screen/work space. To me, a Pro computer should have the most capability crammed into it, and today, Optical is still a regularly used capability. But that is just me, can't decide other people's use of course, and don't want to offend anyone by saying what is or is not Pro"