Examples as to what a company would use that an ASA doesn't provide?
ICMP redirect, policy-based routing, and GRE tunnels, to name 3.
There are more, but those are the biggies that ASAs don't do and that SMBs are likely to need.
Someone who only needs them to firewall (routing handled by a layer 3 switch or a multi-tiered network) can get away without those features, for the most part, or someone who only needs a VPN gateway...these two conditions would be the ones under which a 5520 would be useful. But a SMB that may move to an MPLS setup or may require more advanced features will see their investment turn up as useless.
Either way, the Juniper SRX100 is cheaper and more feature-rich than an ASA5505, and would be my recommendation if the company does not want to spend money on an IOS router with Advanced Security featureset.