Having recently started watching what cycling I can on television I've found that what I thought I knew about cycle racing (based on watching the tour each year) isn't as much as I thought. for instance there seem to be a lot of races on around the same time with teams from the same sponsor competing in each. Why do riders compete in one race but not the other e.g. Froome in Oman and Wiggins in Andalucia. Also apparently there are 'classics' and 'grand tour' riders who may be in the same race but have different objectives. Is there a 'bluffers guide' out there which can help fill my knowledge.
p.s. since most of the action is seen from a moving motobike or helicopter and the cyclists all wear the same kit with helmets and sunglasses why don't they wear numbers to aid identification?