Doesn't this ruling of the SCOTUS nullify this attempt of a balanced and fair election campeign?
Not really. The SCOTUS ruling just said that corporations and organizations (Unions) can buy ads, the people still have to vote to elect the electors. And besides, the ruling is very moot. After the passage of the last law to reform it, the money still found a way in with the 527 groups (named for a subsection of the law). So instead of being "sponsored by Moveon.org" an ad will be sponsored by "GE". It will still be there, just from a different source.
Are those companies bound to addvertise in all regions like candidates have to tour all regions?
No. Candidates are not required either (many 3rd party Candidates are not on the ballot in all states). They can pick out a point they do not like and direct the ad to that area. An easy example is if one candidate is against coal mining. A coal mining company can run an ad in West Virginia pointing that out.
I am curious how this will look during the next election. Too much intertwining of busines and politics never ends well, and I for one wouldn't want to have some billionaire who draws the strings from behind the scenes because it's his constitutional right.
The fallacy that Obama was playing on is that there was no money in it before. There was (through the 527 groups). The only real difference is that instead of saying "Sponsored by..." an organization, it will be a company. The money never left, just the way it got there. And the ruling, contrary to what Obama said, only overturned the McCain Feingold law which is only about 10 years old.