The reporting of the recent Microsoft announcement regarding RSS support seems to conflate and blur the three completely separate things being announced.

1. An IE 7 feature (later this summer). Adds RSS feed auto-detection, just like Firefox and Safari and Opera already do. This could be categorized as "supporting RSS".

2. RSS Extensions (part of Longhorn, so available in a couple of years). These extensions to the RSS format basically allow for different ordering of data (non-chronologically-ordered) to be specified in the stream. This could be categorized as "extending RSS". The open question here is whether this becomes a corrupting influence on RSS compatibility; this could happen if the extensions tend to break existing RSS parser code (see this) or if it leads to haphazardly implemented extended data becoming common in RSS feeds.

3. Windows OS APIs for a system RSS feed store (also unavailable until Longhorn release in a couple of years). This would provide Windows programs with a common way to share feed data. This is only of interest to developers of Longhorn desktop applications.