Google - Why Screw Up with Indexing and Not Admit It?

Recently we've seen Google dropping the index page of a client’s site while leaving nearly all the other web pages in the index. There were server errors previously (robots.txt not reachable) in Webmaster Tools but Google had been back spidering the site since the issue was corrected and accessed the home page but not indexed it.

Others have reported seeing no reported errors in Google Webmaster Tools but yet still having their home pages go missing from the index.

Then the client site suddenly went from having no home page in the index to jumping back into the index with PageRank appearing as normal. We've received no explanation and no understanding from Google as to why this had happened.

Now I understand that there will always be technical issues with indexing (due to the size and nature of Google)  but wouldn’t you think that Google would at least mention this issue somewhere or give some practical advice on what can be done to resolve this issue? I’ve looked on Webmaster Central and nothing – not a thing – about this issue.