i would guess that fresh real fruit is a better choice than boxed things...

I would tend to agree with that esp since if you're blending the oranges, you're also getting the fiber and a lot of phytonutrients that don't last very long in oxygen.

as nice as blended/smoothies are - if you are that concerned re the calorie content why not try eating the fruit as it is - although minimal at least

a. you exercise by virtue of the actual eating

b. it lasts longer than just drinking it back and so you get the enjoyment for longer (well thats so long as your not making something yucky like say broccolli and celery juice)

It's a possibility that they diluted the juice from the carton.  Makes sense since I find that oranges themselves are sweeter than from-concentrate orange juices

and also, often the juice is made not just from the pulp but also from the skin - i suppose the skin has less sugar

People always seem to confuse added sugars from the naturally occuring sugars in fresh fruits.  Don't think of the sugar content in oranges the same way as you would the added sugar in a carton of juice, or anything else for that matter.  Naturally occuring sugar from fruit is packed with vitamins, minerals, and nutrients, many of which help speed up the metabolism of sugar, making such sugars no problem for the body to digest.  Then there are added sugars which are nothing but additional calories typically packed into foods that lack the nutritional attributes of fresh fruits. 

While you should never go too overboard with anything, there is pretty much no limit to how much fresh fruit you can have in a day.  Don't let the sugar content deter you.  Always go for the fresh fruit over the carton juices or anything else of the sort.