Joe and PX are somewhat right but not complete.
ABEC is not related to inline skating or skateboarding. It is a related to precision to prevent vibration in high speed machinery. It can have an indirect relation to quality in that people who make very precise bearings usually put some care into making them. I the early days of skating there were many companies that use "precision" bearings. Precision is an industry grade that basicly says that the bearings roll but can be sloppy or very poor. ABEC became a marker of good quality.
Some of the best bearings by companies like Bones, ZeroDrag, andTwinCam were designed to be better rolling by deliberately violating the requirements of the ABEC ratings.
The companies that sell ABEC rated bearings are not selling you factory "spare parts". They may not have the ability to spend the money or skills to design their own bearings and have a bearing maker do the custom work for them. So they look for a bearing maker that has a stock bearing that fits their needs.
I know the owner of ZeroDrag. The bearings are made by a major US bearing manufacturer and the upper end bearings were designed by the manufacturer's engineers to his specs.
If your board is slipping out from under you, you might want to slow down your bearings a little. The lubricant in the bearing has more to do with it's rolling speed than the grade.
If you find some cheap bearings with grease, it will slow down your board till you get the tricks back, then put your good bearings back in and fly again.
If you don't want to buy more bearings or want more control over the speed, just open up your bearings (you can leave the inside shield off since dirt cannot get in from there) and put a little grease in them. Try it out and see if you want more.