This is a really interesting debate. (I have just read the whole thread while putting DD2 to bed - breast feeding).
I do think that as a slogan "every ounce counts" works really well, or whatever it was that suggested earlier, but without the tesco connotation. It is true without demonising anyone who, for whatever reason, has introduced formula. I think it is very supportive of the struggling new mother, it recognises the importance of bf (in the same way tesco recognises 'every little helps' in these hard times), but without actually promoting ff. Breast feeding is normal and should be the default for human babies, and it is best, but both statements are potentially patronising to the already highly hormonal and emotional newly delivered.
However, this is less about a slogan and more about improving breast feeding rates. The slogan does belie an ideal though so the catchier the better.
Someone up thread posted that hcp support is often rubbish and I'll-informed, and it is. DD1 was very prem and one nurse was fab: happy to let her lie on me, and actually said 'best thing for her and it will promote bf even if she isn't doing it', while the others told me not to feed any more than 4 hourly as they had got her into a nice routine for me 
and what was she doing out if that incubator again! (She came home ebf on demand, not 4 hourly, fwiw). To be told I was doing the right thing, meant worlds to me, even if I hadn't managed to ebf, because every ounce counts.
I think predominantly bf rates are rubbish because of the many myths about it, that fuel cultural distaste. The 'bf is easy/painless/wonderful' is the one that gets me the most. It is not any of those things until it is established, and anything worthwhile takes a little effort, right? Once you are established you may think it is those things, but if a new mum expects that in the first month, then is it any wonder that they change their minds and immediately think they can't do it? There may be reasons that it is particularly difficult but I think it's easy to say there's a problem (whether there is or there isn't) to absolve the inevitable guilt when the decision to give up is made, and that is really sad - both the belief of can't and the ensuing guilt.