Oh don't you worry about that richardm !! This is a constant, at times very amusing struggle between the two parts of Switzerland, how we pronounce what.
There is no right or wrong way to pronounce coop. Just pronounce it like the people around you say it.
Of course it sounds way nicer with a French accent.
I've never heard a Swiss German pronounce it Co-op but am not sure how the other language regions do it. The cooperative has created companies abroad in partnerships with foreign retailers but is not affiliated with the British Co-op as far as I know.
Migros has a silent S because it's composed of the French words "mi-" and "en gros" ("half-bulk" seller).
Pronouncing "coop" as "koop" reinforces the image that people are concentrated inside this enclosure for fattening and controlled breeding. This is made possible thanks to strategic placement of "Prix Garantie" products near the entrance and on shelves at eye-level.
As for "Migros", I personally pronounce it "my gross", for similar reasons.
I must be really out of it - have *never* heard it referred to in Swiss-German as other than "Co-ohp".
As for the pronunciation you are hearing in Vaud - French speakers are bound to pronounce it differently than Swiss-German speakers, I have heard it referred to (in French) as "Copp".
All the (Swiss-German and the almost naturalised) 'locals' around me say Cope but I can never make myself say it that way. To me, it will always be 'The Co-Opp'.
logically it would be ko-opp if there were two words written like co-op.
as far as i know coop means (correct me if im wrong) co-operation, so it is two words, but now written in one. maybe its a logo/ci/cd-thing. for me its coop. the double-o gets stretched to a long sounding "oh"-> koop.
i remember that we had in german tv mid-80ies coop ads and i found a wiki-entry http://de.wikipedia.org/wiki/Coop_eG plus an coop.de webpage. in those ads they were saying ko-opp. but its the same difference us germans saying Gel but hier its jeehl as the swiss tend to french-ize things. maybe this makes it coop even more...
After coming here from the Netherlands, it was a a little strange to see a supermarket whose name is pronounced "koop". In Dutch, "Koop!" means "Buy!".
My Swiss hubby pronounces Coop as "cope" and Migros "mii-grose"... on my own I would have been inclined to pronounce Coop as if it rhymed with "soup" and leave the "s" silent on Migros.
The linguistic trick with Coop is to form your mouth into an "oooo", not moving your lips, while inside your mouth forming two syllables-- "co" and "op", closing with the "P".
The first thing my relo agent did when I arrived was correct my pronunciation of Coop . . . She said it was 'Cope' and I've stuck to that without problems.
(I don't really understand what people mean when they mention 'Coop' and 'Koop' as different pronunciations)