When that IDF soldier was taken in Gaza I read various sources mentioning the IDF's having kidnapped Lebanese as bargaining chips. It's probably only because Gaza is considered legally occupied territory internationally that the attorney general for israel hasn't signed off on considering the Hamas parliamentarians seized from them to be bargaining chips/ political prisoners.
Note that the 2004 exchange was by noted peacenik and softie Ariel Sharon.
Edit: A source popped up that's helpful.
"The prisoners Hizbullah wants released are hostages who were taken on Lebanese soil. In the successful prisoner exchange in 2004, Israel held on to three Lebanese detainees as bargaining chips and to keep the battle front with Hizbullah open. These detentions have become a cause celebre in Lebanon. In a recent poll, efforts to effect their release attracted majority support, much more even than the liberation of Shebaa Farms, the disputed corridor of land between Syria and Lebanon still occupied by Israel."
http://www.guardian.co.uk/israel/comment/0,,1821036,00.html