North Korean authorities arrested Ling, 32, and Lee, 36, in March, saying they had crossed the border with China illegally "for the purpose of making animation files to be used for an anti-DPRK [North Korea] smear campaign over its human rights issue".
The two who worked for the California-based Current TV co-founded by Al Gore, who was Clinton's vice-president, were found guilty after a trial and sentenced to 12 years of hard labour in June.
The visit by Clinton was the highest-profile US contact with North Korea since he sent Madeleine Albright, the then-secretary of state, in 2000.
But Washington insisted that the former president was acting as a private citizen and the trip was limited to securing the freedom of Ling and Lee.
"We have always considered that a totally separate issue from our efforts to re-engage the North Koreans and have them return to the six-party talks and work for a commitment for the full, verifiable denuclearisation of the Korean peninsula," Hillary Clinton said at Wednesday's news conference.
However, North Korea's state-run KCNA news agency said Bill Clinton had apologised on behalf of the women and relayed a message of gratitude from Barack Obama, the US president.
It said that the visit would "contribute to deepening the understanding between the DPRK [North Korea] and the US and building the bilateral confidence".
Christopher Nelson, an Asia analyst in the US who edits the Nelson Report on international affairs, told Al Jazeera that more than just the release of the two journalists needed to have come from the visit for it to be considered a success.'Propaganda coup'
He said the North Koreans "definitely wanted the propaganda coup of getting [Clinton] to go there and show respect to Dear Leader - to the leader of North Korea - and ... they got that in spades".
"So people here [in the US] are worried, with cause, that if all we get are the two women being returned - and we're personally thankful for that, of course - then maybe we gave the North Koreans a little too much."
|Hillary Clinton said the journalists' release was not linked to the nuclear talks [Reuters]
"We'll need to see 'what next'. Did sending somebody of the stature and importance of Bill Clinton, does that serve as a door-opener, a bridge-opener ... a face-saving vehicle for the North Koreans to come back to talks about denuclearisation?"
Daniel Sneider, an associate director of research at Stanford University's Shorenstein Asia-Pacific Research Centre, said there had been weeks of quiet negotiations between the US state department and Pyongyang.
Clinton "didn't go to negotiate this, he went to reap the fruits of the negotiation", Sneider told the Associated Press news agency.
Relations between North Korea and the US have worsened following Pyongyang's second nuclear test on May 25 and consequent United Nations sanctions.
North Korea pulled out of six-party talks on its nuclear programme, expelled nuclear inspectors and test-fired a barrage of missiles in defiance of the sanctions.
It also repeatedly issued bellicose rhetoric against South Korea and the US, but indicated last week that it was open to direct talks with Washington.
The US has maintained that the six-party arrangement is the appropriate forum for dialogue.