disableObjectResizing just on tables

That's not configurable by settings. But I think maybe it could be possible. Search in source files for what disables object resizing. If you find something, write a plugin, ask for table element and disable

//something like this:
var table = element.getAscendant( 'table', true );
if(table) {
    //code for disable
}

I don't know whether it work's, you have to try it.