Question about wireless SOHO routers as access points

So, I've successfully configured some wireless SOHO routers as access points and they all work fine. I've done this with various brands of routers, including Linksys, Netgear, Belkin, and D-Link.

One thing I've noticed is sometimes I'll experience poor wireless performance with the SOHO router configured as an access point. For example, a wired Internet connection might yield 18MBps download speeds and a wireless connection, through a wireless SOHO router configured as an access point, to the same broadband modem will yield 1.5-2MBps download speeds.

Of course, a wired connection will be faster than a wireless one but my question is: is there anything inherent to configuring a wireless SOHO router as an access point that would cause a degradation in performance? I would think there wouldn't be but I'm asking the question here. :)

The process I've used to configure the wireless SOHO router as an access point involves assigning the router an IP address within the subnet of the main router but outside of its DHCP assignment range, disabling the DHCP server in the wireless router, and configuring the wireless settings the way I normally would, in terms of SSID, security, etc.

Thanks!

Peace...