Tại sao Google nói Mozilla Thunderbird kém an toàn hơn?

I have never had problems using Gmail with Thunderbird, but while trying to use a free software client for Google Talk/Chat/Hangout I discovered the following unexpected statement. According to Google’s document on Less Secure Apps:

Some examples of apps that do not support the latest security standards include […] Desktop mail clients like Microsoft Outlook and Mozilla Thunderbird.

Google then offers an all-or-nothing secure vs. non secure account switch (“Allow less secure apps”).

Why does Google say Thunderbird does not support the latest security standards? Is Google trying to say that standard protocols like IMAP, SMTP and POP3 are less secure ways to access a mailbox? Are they trying to say that the activities users engage in with the software puts their accounts at risk or what?

Secunia’s Vulnerability Report on Mozilla Thunderbird 24.x says:

Unpatched 11 percent (1 of 9 Secunia advisories) […] The most severe unpatched Secunia advisory affecting Mozilla Thunderbird 24.x, with all vendor patches applied, is rated highly critical (apparently SA59803).

It is because those clients (currently) do not support OAuth 2.0. According to Google:

• Beginning in the second half of 2014, we will start gradually increasing the security checks performed when users log into Google. These additional checks will ensure that only the intended user has access to their account, whether through a browser, device, or application. These changes will affect any application that sends a user name and/or password to Google.
• To better protect your users, we recommend you upgrade all of your applications to OAuth 2.0. If you choose not to do so, your users will be required to take extra steps in order to keep accessing your applications.
• In summary, if your application currently uses plain passwords to authenticate to Google, we strongly encourage you to minimize user disruption by switching to OAuth 2.0.

Source: New Security Measures Will Affect Older (non-OAuth 2.0) Applications (Google Online Security Blog)