BBC stands for blade brake control. When the operator is mowing and releases the handle and bail the blades stop turning, but the engine remains running. Whereas on a zone-start mower, the engine and blades shut off when the operator releases the handle and bail, requiring the operator to re-start the engine.
Yes, hi-vac model production was discontinued in 2010 due to weak demand. The model remains on our site because some inventory remains at dealerships, although availability is very spotty. The 22188/98 model is equipped to bag and mulch, whereas the hi-vac model was a dedicated bagger (part of its demise). Both mowers are BBC models, bag size is comparable and engines and fuel tank capacity are the same. You can't go wrong with the 22188/98.
-The Toro Company