Hi Nick,
Believe it or not, you can actually have space created where your teeth used to be, and have dental implants (or bridges) placed to replace those teeth. However, the process is involved and takes time...and without an exam it's not possible to know if you're a candidate for this type of treatment. I personally don't provide the treatment, but you can go to FaceFocused dot com and learn more. It's a controversial topic in orthodontics.
I won't go so far as to say that 'no one' should have 4 premolars removed for the sake of aligning their teeth. Nor will I even say you shouldn't have had yours removed...I haven't seen any photos to know for sure...and even then I don't know what your situation was like 15 years ago...BUT...
In my opinion there are VERY FEW people who would benefit more from extraction of premolars than being treated without extractions. OK I'll say it...almost zero! There are two primary factors involved: how much space is needed for the existing teeth; and how much space is available in the jaws? The problem for many people is...not enough attention is paid to the second question between the ages of 7 and 12, when favorable jaw growth can be encouraged.
Think of it this way, using a metaphor. If you imagine the teeth to be like "cars", and the upper and lower jaws to be like "parking decks", you want to make sure the upper and lower decks are built big enough so that all the cars can park straight, right? Well, if more growth is needed, it's best to occur at ages 7-12, with functional dento-orthopedic appliances (expanders, active retainers, etc). Then, when the permanent teeth come in, there is more room to "park the cars" in good alignment, making the orthodontist's job much easier.
In many cases, however, there is less attention paid to the growth of the jaws (perhaps by parents as well as dentists/orthodontists), and a more traditional approach was to wait for the permanent teeth to erupt into the mouth, then just straighten them with braces. Problem is, by the age of 12 it's much more difficult to stimulate needed jaw growth...so, out with the premolars!
The resulting problem is often that MUCH more space is created than needed to straighten the teeth (few people have enough crowding to equal the width of two permanent premolars)...so the only way to close the spaces is (you guessed it) to SHRINK the arch by bringing the teeth together. This creates a less esthetic (my opinion) facial profile, a smaller intraoral volume, less room for the tongue, altered biting angles on the lingually tipped teeth, etc.
The trend to remove premolars has definitely decreased over the years, but some doctors still subscribe to it. And there are always exceptions when extracting premolars may be a good option, albeit very few in my opinion.
I hope this helps...again, it's a bit controversial among dentists and orthodontists, so you will get varied opinions ranging from "you're just fine!" to "that should never have happened". I can't tell you my opinion of your situation, but Dr. Hang at the above referenced site can give you his expert (biased against extractions) opinion on how fesible it is to replace your teeth.