On checking the AsiaMiles website, it seems that only certain airlines will give 100% miles on most economy class fares, here are the breakdown:
Cathay Pacific Airways
Y/B/H/K/L/ M/W
100 % miles earned
Aer Lingus
Y/B/H/K/M /W/L/O/Q/ V/N/G/S
100 % miles earned
American Airlines
X/Y - 100% miles earned.
B/C/H/K/M/R/W - 50% miles earned.
British Airways /
Deutsche BA
B/C*/D*/Y/ H/K/L/M/W
100 % miles earned. * For domestic UK only.
Finnair
B/Y
100 % miles earned.
H/K/L/M/W
50% miles earned.
Iberia
R/Y
Only above earns 100% miles.
LanChile
Y/B/H/G/K/L/M/N/O/Q/S/V/W
100 % miles earned.
Ansett New Zealand
Y
100 % miles earned.
K/L/M/N/O/Q/V
50% miles earned.
Dragonair
Y
100 % miles earned.
B/H/V
50 % miles earned.
Japan Airlines /
Japan Asia Airways (International)
Y
100 % miles earned.
B/G/M/N/Q/X
50% miles earned.
Japan Airlines /
Japan Asia Airways (Domestic)
J/Y
100% miles earned.
A+/I
50% miles earned.
Qantas Airways
Y
100% miles earned.
B/H/K/L/M/W
50 % miles earned.
Sabena & Swissair
H/K/L/M/Y
100% miles earned.
B/V
50% miles earned.