Curry leaves (Kari plant) is native to South India and Sri Lanka and is essential to cooking styles in the South and South West of India.
As most BIR cooking styles originated from Bangladesh (1000 miles North of Sri Lanka), my guess is that curry leaf was/is not an essential ingredient.
As SS pointed out, most curry powders already include some curry leaf powder.
I also read somewhere that in Indian cooking, 1 fresh curry leaf = 6 dried curry leaves.
As fresh curry leaves are quite difficult to obtain here in UK, I guess not many BIR's would use them anyway.
SnS ;D