Nothing laughable there - it can be used as an uplink to a NAS, meaning that two 1 GBps clients would be able to fill 2 Gbps off that NAS's 2.5/5/10 port. That uplink can also be used to connect to another 2/5/10 Gbps switch, and once again multiple clients connected to the router will be able to concurrently saturate that 2.5 Gbps port.
Or, you could use it in Dual WAN mode, and connect a 2 Gbps uplink to it (yes, 2 Gbps Internet services exists in Asia).
This kind of architecture is very common. Most high performance switch first hit the market with only a few higher speed ports, and gradually as price/performance improves, switches gradually start supporting more ports. Remember how the same thing happened when Gbps Ethernet started - your switch would have 2 or 4 Gbps ports, and the rest would still be Fast Ethernet.
This design isn't an Asus decision, it's a Broadcom limitation. The chip lacks the performance to route more traffic than that.