IMO, it's better to watch what pages are actually getting Google traffic anyway and work your improvements from there. But if you want to know whether any specific URL is indexed, the surest information will be to put the full URL in the search box and see the answer. Even then, it might be indexed at one data center and not another.
I noticed the same thing a couple of days ago. Both with my biggest site and a couple of other sites I'm following closely. I have investigated it a little, and my conclusion is that they are either 1) not interlinked good enough, or 2) the titles were too much alike (i.e. the three first words were the same). I have made some improvements now, so lets see.
Do you think this can be your problem too?
About tedster's comment - I haven't noticed a drop in traffic, but the pages are definitely gone.
Hi Venunath...very true, the number of pages are reducing everyday. I fail to understand why and it is also effecting the website ranking and traffic. I hope things get back to normal. I have tried everything....webmasters tools, analytics and n number of website diagnostics sites...but with no success. Have you also experienced drop in traffic.