Q:

Why is file transfer to the phone via WiFi so slow?

I have two computers, C and W. 

C connects to the router with a cable
W with wifi. 
Transferring a 355MB file between C and W takes 62 seconds, 5.7 MB/sec. LAN and FTP speed is the same.
Copying the same file to my phone from C, running Total Commander for Android on the phone with the LAN plugin takes 456 seconds, 780 kB/sec.
If I use the FTP plugin, 96 seconds is enough, 3,7 MB/sec.

Why is standard copy much slower than FTP? Why is FTP transfer 54% faster to W than to the phone? What can I do?
C and W run Win 7, the phone Android 2.3.4.
C uses FileZilla as FTP server.

A:

Every protocol has overhead. The "LAN" copy you're talking about it most likely SMB/CIFS. CIFS is quite prone to being badly configured(and thus slow) and overall has more overhead than FTP. 
FTP is a very simplistic protocol. It's hard to get it wrong. CIFS is a complex protocol, most likely the implementation on the phone is either limited or slightly wrong. Not bad enough to cause a failure or anything, but rather just slower
Based on comments:
The speed difference you are seeing between wireless and USB is to be expected. USB 2.0 has a maximum speed of 480Mbit/s or 60Mbyte/s. In comparison, wireless G's maximum speed is 54Mbit/s and even wireless N is either 144Mbit/s or 300Mbit/s depending on configuration. Most phone wireless chipsets have a speed limit built in due to cost-saving(in power or price) measures. For instance, I can't get over 20Mbit/s with my phone which implements wireless G. 
Also, one more thing to keep in mind is that usually when you use a USB cable to transfer files, it can take a lot of short cuts. All it has to do is expose the SD card at a block-level, not parsing file systems or worrying about protocols. The speed difference due to this is probably negligible, but I'm sure it's measurable. 

