Have the words stout and porter become interchangeable?

As you may have read I've recently started a love affair with dark beers. Even the rising temperatures have not been able to tempt me towards light spring beers. One thing I have noticed however is the interchangeable use of the terms stout and porter.

First a little history lesson. Porter was originally named so because it was popular with river and street porters. Stronger variations of the style were known as Stout Porter, Double Porter or Imperial Stout Porters. Eventually the porter was dropped and these stronger beers began simply being known as stouts. 

After reading up on the style I decided to look back through the bottles I'd been drinking and see if there was actually any correlation between the use of the word stout and being of a higher strength. While I didn't find any  meaningful correlation, I found porters ranging from 4-11% and stouts from 5-10.5%, I did notice that the large majority of the "flavoured" beers (chocolate, cherry, raspberry, chilli etc) I'd had were stouts rather than porters. I have to point out here that I thought the Bristol Beer Factory Raspberry Stout was delicious. It was like a black forest gateau in a pint.

Maybe this doesn't mean anything, maybe I'm looking too deeply into something which really has no relevance but hey it kept me entertained for an hour or so.