Kiltrash
Yes, but you can turn wifi back on above 10,000 feet separately while the device's other transmitters remains in airplane mode. I personally doubt most people turn-off their wifi on descent. Most phones run between 1-2Watts in cellular mode but less than .02Watt in wifi and the frequency bands are different. Large difference in power output.
Even if you don't use your phone's wifi, there is still a wifi access point on aircraft that offer such service and that is transmitting in and of itself. The FCC is considering rule changes allowing cell phone calls at altitude and below 10,000 feet due to 'advancements in technology'. Get a good set of noise cancelling headphones or ear plugs if they relax that rule. I got a taste of that back in the 90s when much of United's fleet had a GTE Airfone on the back of every seat. The only reason it wasn't more objectionable is that it rarely worked and was incredibly expensive.
Just FYI, there were two parts to the original issue of cell phone use on planes - possible interference with aircraft instrumentaion (shielding on older equipment just wasn't made to filter out spurious RF from the newer frequencies) but also confusing ground cell towers due to the rapid hand-offs as you cruise past towers every few miles. I don't think today's mobile infrastructure (ground) would be able to handle everyone on every plane on their phones.