Yes, D90 was more advanced. The D70 had an electronic shutter for fast speeds, doing the timing by enabling the CCD sensor for only the shutter time (which was in fact the shutter). This is what compact cameras do too. There are pros and cons, and these also do have a simpler mechanical shutter, used for slow shutter speeds (generally about 1/100 second and slower), but otherwise it is mostly only a protective covering to keep light off of the sensor. Blooming was one fault in electronic shutters.
The D90 used an actual high quality mechanical focal plane shutter, capable of the faster speeds.
Technically, there is more. The D70 was a CCD sensor, and the D90 (and all current models) use a CMOS sensor. CCD must be disabled each shot, to move the image out of them, so they can use this as a shutter too ( a free shutter). D40 and a couple of other inexpensive models were the same.
But now CMOS sensors are used, and it is better, but much more complex, and is not suited to serve as an electronic shutter. Focal plane shutter is also better, but has its own limitations too.
This would cause the blooming issue in electronic shutters. The CCD chip was enabled only 1/8000 second for the exposure, but the simple slower mechanical shutter would be open 1/100 second... letting the bright light hit the chip 80x longer, and which caused blooming (sort of a smear of bright objects).
A focal plane shutter is only open the 1/8000 second. (***** I think you meant 1/4000th)
Here is an example of blooming. D70 and D80, both use the same CCD sensor, but D80 (more advanced) uses a real focal plane shutter.
Nikon D80 Review: Full Review - Exposure