CALL it a combination of financial need or greed, and exploding demand: As of last month, 21,000 flats had been rented out by Singaporeans, a near 60-per-cent spike from the 13,200 units just 17 months ago. Coming as it does three years after subletting rules were relaxed, Housing and Development Board chief executive Tay Kim Poh attributes this recent surge to changing market dynamics. "Rentals for...