Because the network cards in them may not be capable of delivering the speeds. I can't tell you what they are as you haven't given the model number.
These are the real-life average speeds you can expect from wireless devices:
802.11b - 2-3 Mbps downstream, up to 5-6 Mbps with some vendor-specific extensions.
802.11g - ~20 Mbps downstream
802.11n - 40-50 Mbps typical, varying greatly depending on configuration, whether it is mixed or N-only network, the number of bonded channels, etc.
802.11ac - 70-100+ Mbps typical, higher speeds (200+ Mbps) possible over short distances without many obstacles, with newer generation 802.11ac routers, and client adapters capable of multiple streams.
Whether they connect on the 2.4Ghz or 5Ghz band can also make a big difference.
The Advent will most probably be at the lower end of the above. The HP most probably 802.11b/g/n.
Like I said, connect to the hub with an Ethernet cable and see what speeds you get. Don't know about the HP but the Advent will have 10/100 Ethernet, best you'll get from that wired will be 80 or 90.
Dave.