half truth statistics coming from Secunia.
1) Reported vulnerabilities are not the same thing as unpatched reported vulnerabilities and Google moves pretty quick to patch things.
Their bounty rewards program helps A LOT with finding and reporting vulnerabilities - this is an incentive for people to smash, crunch and otherwise torture the browser in every imaginable way to see if it sprouts a leak, and that leak will be patched for the benefit of all the users.
I don't see the other mentioned browser markers offering such bounties.. MS in particular is known for the secretive way in which it shoves stuff under the carpet (they have a sort of bounty rewards program.. with a NDA with stupid terms attached) when it doesn't like it shown until they release a patch for it, sometimes years later, and bragging about finally fixing x or y while some things never get fixed or get stealth "unsupported" half-fixes (*cough* POSReady fixes allowed for WinXP on purpose - they could easily nuke it.*/cough*).
2) i'm a Secunia PSI user and i can tell you that their detection of the installed Chrome version is crappy about half of the time.
This is because Chrome keeps the previous version around when it installs an update, just in case you need to roll back. If you have Chrome installed and if you ever applied an update to it, just take a look at C:\Program Files\Google\Chrome\Application (or wherever you installed it). You'll see there 2 folders, one for the current version and one for the previous version that you had before the latest update.
Sometimes Secunia PSI will detect the version that was present when i started the computer and keep pestering me to update it even if i just updated it. When this happens i have to manually FORCE a full system scan in Secunia PSI just so that it can detect the updated version.