The theory goes that a country like US/UK/Japan/etc always has the capability of paying their $/£/¥/etc debts (modulo political idiocy like the US debt ceiling standoff). Of course it might be painful from an inflation standpoint, but that would always be better than a default. Therefore the interest-rate relates to the risk of inflation making the repayment less valuable, not the risk of a literal default.
Since individual eurozone members don't have that privilege, their interest rates are high leading to a potential death spiral (risk of non-payment -> rates go higher -> debt more expensive -> risk is now higher) The theory behind the "eurobond" solution is that since the ECB can print euros it would remove the default risk so in theory interest rates would be limited to inflation risk.
You make a good point about the business climate numbers though. I don't see how a guaranteed-in-common Eurobond is ever going to fly with economies like Greece in the mix. Italy probably has some hope of reform if they want it badly enough, but it would be a big step for them.