I assume it´s because when they started out the Nobel Committee consisted of members of the Storting or people associated with it. The first director of the Nobel Committee was legal counsel to the Storting in Sweden. Also tradition had it that the King of Sweden would pick the members on the Nobel Committee. Well, at the beginning, he did. And I guess they didn´t want to have a role for the Norwegian Royalty and never changed it so that the King would play a role in the ceremony itself.
I found this
"In Norway, during the years 1901-1904 the decision on the Peace Prize was announced at a meeting of the Storting on December 10, after which the recipients were informed in writing. On December 10, 1905, the Nobel Institute's new building at Drammensveien 19 was inaugurated in the presence of the Norwegian Royal Couple, and it was announced that Bertha von Suttner had received the 1905 Peace Prize. The Laureate herself was not present"
So the Norwegian royals always played an observing part in various ways but never actually handing out the prizes.
" Until 1960 the Chairman was chosen from the small group of "Gentlemen of the Realm" - prime ministers, ministers for foreign affairs and other high officials."
AP
OSLO, Norway - [size=-1] Tom Cruise and Oprah Winfrey will continue the tradition of bringing a superstar shine to dark December nights in Norway when the pair hosts the annual Nobel Peace Prize Concert. [/size]
[size=-1]The Saturday concert, held to honor Kenyan environmentalist Wangari Maathai, will also feature musical artists such as Joss Stone, Andrea Bocelli Diana Krall, Cyndi Lauper and Patti LaBelle. [/size]
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The 64-year-old Maathai, Kenya's deputy environment minister, was honored as founder of the Green Belt Movement, which has sought to empower women, improve the environment and fight corruption in Africa for almost 30 years. [/size]
[size=-1]Winfrey said it was a "great pleasure" to celebrate "the first African woman recipient of one of the most meaningful awards of our time." [/size]
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"Wangari Maathai is a true inspiration because she uses her life to benefit others, from fervently fighting for women's rights to literally turning the earth to improve living conditions in Africa," Winfrey said. [/size]
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Cruise said he was "exceptionally proud" to pay tribute to Maathai. [/size]
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"Wangari is a real example of what one person, determined to help her fellow man, can accomplish," he said. "She has demonstrated that change in conditions can occur simply by one's willingness to roll up their sleeves and do something about it." [/size]
[size=-1]The Nobel concert, which will be carried live in more than 100 countries, will be broadcast in the United States Dec. 23 on E! Entertainment Television. [/size]