グリニッジ男爵という位について：エリザベス女王の夫へ与えられた称号ですが、女王の夫ならば、公爵（Duke)とか、伯爵（Earl）の位を作って与えるのが自然だと思うのですが、どうして、男爵という一番低い爵位なのでしょうか。グリニッジ公爵でも良いと思います。

別にエディンバラ公爵など、男爵以外の爵位を持っているからでしょうね。

グリニッジは公爵位ではないからです。
http://en.wikipedia.org/wiki/Baron_Greenwich

グリニッジは：
http://en.wikipedia.org/wiki/Greenwich

Greenwich is notable for its maritime history and for giving its name to the Greenwich Meridian (0° longitude) and Greenwich Mean Time. The town became the site of a royal palace, the Palace of Placentia from the 15th century, and was the birthplace of many Tudors, including Henry VIII and Elizabeth I. The palace fell into disrepair during the English Civil War and was rebuilt as the Royal Naval Hospital for Sailors by Sir Christopher Wren and his assistant Nicholas Hawksmoor. These buildings became the Royal Naval College in 1873, and they remained an establishment for military education until 1998 when they passed into the hands of the Greenwich Foundation.

元々王宮があり、建物がだめになってサー・クリストファー・レンによって再建され、王立海軍大学となり、1998年までずっと英国の軍隊の教育機関のエスタブリッシュメントだった。そういういわれのある土地ですから、決して「そのへんの町」ではないですね。

プリンス・フィリップの肩書き込みのフルネームは、

His Royal Highness The Prince Philip, Duke of Edinburgh, Earl of Merioneth, Baron Greenwich, Royal Knight of the Most Noble Order of the Garter, Extra Knight of the Most Ancient and Most Noble Order of the Thistle, Grand Master and First and Principal Knight Grand Cross of the Most Excellent Order of the British Empire, Member of the Order of Merit, Companion of the Order of Australia, Additional Member of the Order of New Zealand, Extra Companion of the Queen's Service Order, Royal Chief of the Order of Logohu, Extraordinary Companion of the Order of Canada, Extraordinary Commander of the Order of Military Merit, Canadian Forces Decoration, Lord of Her Majesty's Most Honourable Privy Council, Privy Councillor of the Queen's Privy Council for Canada, Personal Aide-de-Camp to Her Majesty, Lord High Admiral of the United Kingdom.

だそうです。じゅげむみたいですね。
http://en.wikipedia.org/wiki/List_of_titles_and_honours_of_Prince_Philip,_Duke_of_Edinburgh