good observation about tasting the yogurt.
the truth about frozen yogurt is that it's NOT really healthy. It's not really 100% yogurt. To make it taste good, like dessert, a huge amount of sugar is added and the actual % of real yogurt in a froyo is questionable. It's more transparent in the US so I am aware that some frozen yogurt includes only 15 - 30% real yogurt and the rest is cream and sugar (basically ice cream). an article in a chinese magazine exposed all of this a few months ago, and it featured crumbs, yomama and another one I forget. basically saying that these shops are using deceptive advertising.
in the US, the govt bodies limit what frozen yogurt shops can claim and limit the ingredients that can qualify as frozen yogurt. in HK, there is no one protecting the public so most of them lie and talk about how healthy froyo is when most it has only 20% or even less of real yogurt. but I guess it's better than nothing!