Why do deciduous trees shed their leaves in autumn, but conifers do not shed their needles?

Deciduous trees lose a lot of water through evaporation from their large and thin leaves. In summer, this does not pose a problem, since the roots soak in enough water from the soil, but in winter this is not possible because the soil is frozen. If the leaves are not shed before winter, the water will continue to evaporate and the plant will dry up. 

Moreover, the leaves can become brittle with frost and crack. Therefore, the deciduous trees shed their leaves as a precautionary measure. In contrast, the needles of the conifers are leathery and small, and there is very little evaporation through them. The needles are also frost-proof and stop their growth in winter.