Actually in all those Download managers you mentioned,Download status is shown in KB/s
So you are getting 30*8=240Kbps.Or when you are downloading,in the status bar is it shown 0.4 kBps?
Even 240 kbps is slow speed for 500 BSNL home plan.I get 200KBps ie 1600kbps while downloading.
The problem may be due to the TCPIP.SYS patched into your system.If you are using a pirated OS prolly the max half open connection may be set to bogous values which do not affect torrents but affects direct download.
Download lvllords patch and change the value to 50.<---Pls use
www.google.com
And the head over to
www.speedguide.net and download and instal TCP optimiser.
That should solve the problem.