1) there is no such a direct link between two routers located in two Internet eXchange Points-IXPs (even in same city) if they are from different ASes. For example, a router A belongs to AS x located in IXP1, and router B belongs to AS y located in IXP2, there is no link between A and B.
it is not safe to assume that routers A & B, each belonging to a different isp and each in a different colo in the same city are not otherwise interconnected.
2) small AS will not use one router to connect to 2 different providers in differnet IXPs. It is much cheaper using one router to connect with different ASes in a same IXP.
what if the two providers to which i want to connect are not at the same ix but i can get a cheap L2 transport to the second ix? randy