Last-Modieid and Etag missing from text/html responses

I am working with IIS 7.0 on W2K8 R2 and have seen odd behaviour:

1. From the logs, all requests for text/html documents which include .htm and .shtml files, plus directory/no filename URLs including the homepage (GET /) are getting 200 responses
2. Running an HTTP trace, I can see all response for text/html resources except for the homepage are missing both a Last-Modified date and an Etag
3. Requests for the homepage do include a Last-Modified and an Etag, although the log file data (point 1) does not suggest clients are receiving a Last-Modified and making If-Modified-Since requests as no 304 responses are being logged
4. Requests for all other file/MIME types *do* include both Last-Modified and an Etag and the logs *do* show 304 responses (and so indicate IMS requests being made by clients)

So I have pieces which do not add-up, I'm aware of that...

• The logs files say all requests for the homepage are receiving a 200 Responses, but
  • I can see Last-Modified and Etag headers in responses for the homepage when I run a trace
  • I can see 304 responses for requests for other MIME types showing the clients must be capable of and making IMS requests which are effective for all MIME times other than text/html

Searching numerous IIS forums and I can people requesting to supress Etags (for believed performance reasons associated with farms that don't appear to relate to IIS 7.0 and above) and it being said that supression is impossible...clearly not!

Has anyone any ideas on where to look for why Last-Modified and Etags should be being omitted from all text/html respsones yet included in all other responses, and why when I snoop an connection I can see the homepage (alone) including Last-Modified and Etag headers in the response yet the log data suggests no IMS requests for the homepage suggesting no Last-Modified and Etag being sent in 'normal request serving', e.g. when I'm not tracing the request/response.

Thanks for any pointers.