Even if you configured multiple static default routes with the command ip route 0.0.0.0 0.0.0.0 x.x.x.x; the router will only select the best path to network 0.0.0.0, and install that route in the ip routing table.
If you do a (#show ip route), you should be able to see the network that the router is actually using to forward traffic to network 0.0.0.0.
As far as been able to ping your interfaces ip address; do you mean from your internal network? Or from the outside?
If you mean from your internal network; the networks connected to your ISPs must be distributed to your internal network through a routing protocol. If they are not distributed into your internal network through an IGP only the network that is configured as the default route will be the only one you will be able to ping, as it seems to be the case.
If you have multiple connections to one or more ISP's BGP might be appropriate might be appropriate because it allows manipulation of path attributes, facilitating the selection of the optimal path.
Excerpt from RFC 2270:
"a problem exists in that many ISPs can only support the load-sharing and reliability requirements of a multi-homed customer if that customer exchanges routing information using BGP-4 which does require an AS as part of the protocol."
If BGP is not an option for you, then I would suggest multiple routers, one for each ISP connection. Then you can use an IGP and route maps to load balance your traffic between connections.
Best Regards
P.S I'm not CCIE, so If there is a CCIE or someone with more expirience that can help clarify this the better.
