Yes, you are right. We actually call a salad with meat and eggs and bacon bits, a Cobb Salad here. I've had a steak and romano cheese salad, which was really good. Generally, I can see why the concept of laying meat on top of lettuce would seem kinda gross, now that I think of it. It should be separate.
Salad Cream, huh? Forgive me, but it sounds kinda like you put it all in a blender and creamed it...or whipped cream is the other picture that comes to mind. Neither one would sound as good as salad "dressing" to me. Salad "dressing" sounds more like the proper "accessory" to a "well-dressed" salad - ha ha.
Yep, Miracle Whip sounds like our version of your tarter salad cream. There's many of us that feel the same way, here....put snugs on our Miracle Whip side ;-)
Here is a link to one interpretation of what Salad Cream is.
The number one seller in Britain is made by Heinz
http://www.bbc.co.uk/dna/h2g2/pda/A505784?s_id=2
Here are details from Heinz's official UK site
http://www.heinz.co.uk/products/heinz_salad_cream.aspx
Here is another link which goes nearer my feelings on Salad Cream - incidently I do not buy the Heinz variety I prefer my local supermarkets own brand.
http://www.icons.org.uk/nom/nominations/salad-cream