Kenko, can you provide links to these three warnings you are mentioning (in your earlier post you said UK, and in this last one USA and Australia)?
I can find nothing in the US Department of State's travel advisory pages (Travel Warning nor Travel Alert) regarding a current advisory for anywhere in Malaysia.
Australia does seem to have an alert, but it's from August 2011, not two weeks ago, and the advice is given as 'reconsider travel' not 'do not travel':
>We strongly advise you to reconsider your need to travel to the islands, dive sites and coastal areas of eastern Sabah because of the high threat of kidnapping by terrorists and criminals. Information of August 2011 indicates that terrorists continue to plan kidnapping operations in eastern Sabah, including but not limited to Mataking, Sipadan, Kapalai, Pandanan and Mabul Islands. In the past, terrorists have kidnapped foreigners from coastal areas of eastern Sabah, the islands and surrounding waters. If you do decide to travel to this region, you should exercise extreme caution.
The UK also mentions the possibility of abduction, but they are citing an event near Semporna that occurred in Feb 2010 as a basis, and there is no indication that there is an imminent threat, and furthermore, they do not word it as a warning, but as a 'caution':
>There are indications that both criminal and terrorist groups are planning violent acts against foreign tourists in eastern Sabah. Of particular concern are resorts located in isolated parts of eastern Sabah including Semporna and the islands of Mabul and Sipadan. This includes transportation routes to and from island resorts. Terrorist groups and criminal gangs have been responsible for acts of piracy and kidnappings of foreign tourists in eastern Sabah in the past. Travellers should exercise caution if travelling in these areas.