The solution may be as simple as placement of the router/antenna, or it may be a configuration mismatch between the MacBook and the router. 2Wire is a fairly common router used by some ISPs, the router might be configured to use IPv4 and the Mac might be configured to use IPv6 (different address schema), or the channeling might be set different (encryption setting mismatch). Since the problem seems to occur mostly with the newer computers, I would lean more toward a configuration problem, but recommend checking the antenna first (this would automatically transfer to a new router), then check the settings. Depending on the environment of the router, the time may have come to get a new one (I have seen some last many years and some last only months).
Check that the following are set the same on the router and the Mac's:
- IP Addressing schema
- Encryption settings
- Channel and frequency settings
If you are going to relace your hardware, I recommend a router with MIMO technology using the 802.11g standard. As far as the 802.11n standard, keep in mind that it has not been approved and published in its final form yet, this could mean that any technology using this "pre-standard" may become obsolete and unusable overnight.