Neil_McRae, welcome to Webmasterworld! IA, for some (most?) is an undesired archive of copyrighted websites, so blocking and or removal requests is more common. However, getting them to index has never been a problem: just have an active website and they will EVENTUALLY get there.
As for site modifications, that question is in regards to many or all of the pages having LAST DATE MODIFIED headers changed. If most are still 2006, it is unlikely IA's bot will spend much time, even with a new robots.txt. Their resources are not anywhere near the big SEs and, by looking at their name and mission, indicates they are more interested in HISTORICAL SNAPSHOTS of websites rather than keeping 100% up-to-date.