It would appear from your description of the IOPC that you don't appreciate the difference between a major "oil producing nation" (Saudi Arabia, Iran, Venezuela, Kuwait, Iraq, etc) and the three nations (US, UK, Netherlands) housing the five major multinational oil companies (Exxon Mobil, BP, Shell, Chevron Texaco, Gulf)
I'd suggest a closer look at the way the IOPC actually works (it will require a trip to the library; the more interesting details of the oil industry are not available online) before pushing your argument any further.
Merely for the sake of humor, I would note that your choice of verb when you say that tanker accidents have "sank" since the 1970's is rather unfortunate.
In your discussion of single-hulled vs. double-hulled tankers, you seem to be unaware of the fact that cheaply-constructed double-hulled tankers suffer from much greater rates of corrosion than the older single-hulled vessels. This is just beginning to make itself felt, as double-hulled ships are only now beginning to fail (read: sink) "prematurely." Again, you'll probably have to go to the library to learn more about this.
Finally, you can beat up on "flag of convenience" nations like the Bahamas all you like, but the fact of the matter is that inspections in even the most "modern" nations are woefully inadequate, and repeatedly pass ships on the brink of hull failure.
Tankers are not cheap, and for various reasons, the big five generally prefer to own and operate their own ships. Furthermore, pretty much every nation on earth wants to have more tankers under its flag, not less. Wagging our fingers when disaster strikes isn't going to change these things.
The notion of some sort of "tanker spill justice" is appealing, but if you want to make a reasonable argument, you'll have to find a way to force five companies in three nations with a proportionately short coastline to pay for the bulk of the damage caused by the oil spilled the the world's oceans every year, of which only a fraction is attributable to gross hull failure.
In short: decent sentiment, appallingly poor research. The oil industry is a huge, complex subject. The more you know, the harder it is to summarize. I do like short articles about Big Oil, but only when they have a very narrow and carefully researched focus.