Actually, SmarterStats has had the ability to be queried for bandwidth since version 2.x (see the Statistics.asmx functions. We added the ability for site data to be queried through web services since version 3.3 in the Query.asmx web service. These are undocumented, unsupported web service calls, and not guaranteed to stay the same with updated versions, but they do work.
To enable the use of this web service, and to prevent people from hammering your server, this web service is password protected. You'll need to load AppConfig.xml in notepad, find the WebServiceAuthorizationCode setting, and put in a password at least 10 characters long. This password will need to be passed to every call to query.asmx.
The query language to use is very similar to sql, but not exactly the same. An example query is:
select * from fTopDownloads(1, '2006-01-01', '2007-08-08') order by hits desc
If you want to get sample query names, to use (instead of fTopDownloads), look in Config/ReportConfig.xml for the QueryName and Default sorts to use.
Because this is an undocumented web service call, they are also unsupported. That said, it should be able to fill almost any need.