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.
However Greece is a totally different graph, it seems that the Euro gave access to cheap credit for the first time and they took as much as they could get. Or some of the former numbers are fake, who knows.
I guess there are two problems: 1) Current interest rates are unsustainably high 2) Unsustainable public policies... Eurobonds would probably solve 1) but increase the danger that 2) doesn't get addressed.
But the interesting thing is (and it was before my time so I'm taking my parents word for it) most of it was created because of the assumption people will cheat on their taxes if they can, so they added a lot of paperwork and 'silly' taxes to make up for it. Most is unneeded now but remains. Most stores are forced to use certified software they can't tamper with. A lot of purchases are done using credit/debit card so they can't be 'forgotten' in the tax forms, but because there is still the mentality of 'business owner' = 'tax evader/thief' a lot of this bureaucracy remains.
I have two examples that for me are just absurd, but if you start a company, even before you start developing a product or whatever you do, even if you don't take a salary or hire anyone, you are forced to pay social security (about 150 euros) and a chartered accountant per month (about 100 euros) before even having any income on the company. This was introduced so business owners couldn't just try and declare no 'profit' and avoid taxes, but now, it cripples a lot of small business just trying to start or hold on.
If you look at the world banks doing business report + transparency internationals corruption report you get: - Iceland: Rank 9 / 13 - Ireland: Rank 10 / 19 - Italy: Rank 87 / 69 - Greece: Rank 100 / 80
No wonder that Ireland+Iceland are doing better, growing again. Even if you forgave Greece+Italy their entire debt, gave them their own currency back etc... I would bet in 20-30 years they would be in the exact same situation as now! I studied in Italy for 2 semesters and I love the country but every time I had to deal with the public bureaucracy I wanted to blow my brains out... I don't know how anyone could run a business in Italy and it is really astonishing how many great companies there are, which shows that a large part of the population has a very good education and work ethic...