Tiger Airways and Silkair are 2 very different carriers. The former is a hard core LCC, no doubt about it. The latter is one confused sandwich.
Silkair, I reckon, will soon function as an airline that connects other international passengers in Singapore through Terminal 2 as their ops are meshed together with SQ
Tiger, operates out of Terminal 1, will be a separate airline altogether.
As far as Temasek Holdings (SQ's owner) is concerned, LCCs are coming whether you like it or not. Rather than letting SQ
/MI lose money to the foreign LCCs, why not create one themselves and let them compete? If SQ
/MI were to lose money, the coins will still fall into Temasek's coffers via Tiger.
That is why u will still find Tiger and Silkair flying some similar routes and singing the same mantra (serving destinations within 4 hours from Singapore).