In most cases, I don't think about it too much. I personally would never use the term "Your are my favorite" on a page with only one of my boys because I do think it clearly shows favoritism, whereas the other statements you referenced could apply to multiple children IMO. My boys NEVER look at my scrap pages. I wish they did, but they are super disinterested.
I don't count my pages, but I do try to think about spreading the love. My older two hate getting their pictures taken and my little guy is just an easier subject to catch right now, so he's featured in a disproportionate number of pages
Plus he's changing so much (he'll be two this weekend).