I appears so but it has been indicated that they have done like AMD did with a new command compression software. Basically allowing everything to be compressed then sent so the memory bus being smaller is not an issue. This is still to be seen but they would need 1/3rd the compression of before to ideally justify the new bus.

AMD's next gpu is said to have a 256bit bus aswell due to the compression

As for the performing worse then the 780ti, if they decrease the number of cores but increase their performance, they can balance out.
750Ti was their first run at the architecture and some improvements have apparently been made on the chip itself. Hence the lower core count. they have increased per core performance which means more overall performance, and reduced the number which reduced the power usage and heat output.

If you factor in a loss of 200 cores, that's an 8% loss overall if it were to have 2200 cores. Boost the performance on the other 2000 cores by a few % and you make up the difference. Therefore allowing higher performance and reduced core count.

Its like putting a 3.3GHz 4 core against a 4.9GHz 3 core, which would win?