There has been some discussion of the differences between the RPM and 
DEB philosophies, in particular Ubuntu LTS and RHEL derivatives such as 
the soon to be defunct SL without clear replacement (hopes for RockyEL 
that probably will not have the sort of support the HEP community 
through CERN/Fermilab provided, or perhaps Princeton Springdale, or even 
hope that the HEP community will re-introduce SL now that CentOS "8" et 
seq. effectively is RHEL semi-beta).  After some digging, I found the 
URL that explains the Canonical Ubuntu philosophy, also as reflected in 
the the release numbering scheme used by Ubuntu.  Please note that I am 
not affiliated with Ubuntu in any way other than as a "user"; this note 
is *NOT* an advertisement for or against any distro, merely a 
clarification as to the "philosophy" of an "enterprise production" 
distro other than SL.

The relevant URL is:

https://urldefense.proofpoint.com/v2/url?u=https-3A__wiki.ubuntu.com_LTS&d=DwICaQ&c=gRgGjJ3BkIsb5y6s49QqsA&r=gd8BzeSQcySVxr0gDWSEbN-P-pgDXkdyCtaMqdCgPPdW1cyL5RIpaIYrCn8C5x2A&m=YHVn3IEuYexuWWwLYQFegF7TqJbRDPX4ksA9J8RXARM&s=gufQbFWexsVtfH5N6GgFQVCYwt6F0XILQwqxNNBOkZA&e= 

(again, note that Ubuntu is NOT a .org or .edu, but a .com).  Currently, 
in the above URL, it is stated:

There is no extra fee for the LTS version; we make our very best work 
available to everyone on the same free terms. Upgrades to new versions 
of Ubuntu are and always will be free of charge.

AND

Furthermore, we define the LTS to be:

     Enterprise Focused: We are targeting server and multiple desktop 
installations, where the average user is moderately risk averse.

     Compatible with New Hardware: We will make point releases 
throughout the development cycle to provide functional support for new 
server and desktop hardware.

     More Tested: We will shorten the development window and extend the 
Beta cycle to allow for more testing and bug fixing

and clearly state that it is not:

     A Feature-Based Release: We will focus on hardening functionality 
of existing features, versus introducing new ones,

End excerpt.

For an earlier version of some of the above, see:

https://urldefense.proofpoint.com/v2/url?u=https-3A__askubuntu.com_questions_1233_whats-2Dthe-2Dmeaning-2Dof-2Dversion-2Dnumbering-2Dof-2Dubuntu&d=DwICaQ&c=gRgGjJ3BkIsb5y6s49QqsA&r=gd8BzeSQcySVxr0gDWSEbN-P-pgDXkdyCtaMqdCgPPdW1cyL5RIpaIYrCn8C5x2A&m=YHVn3IEuYexuWWwLYQFegF7TqJbRDPX4ksA9J8RXARM&s=wBtsyjJjq9cADzvaI2s_dbWk2s23D7sXjoXTrQwNIJ0&e= 

Unlike IBM RH that is forced under the GPL and Linux license to release 
nominally buildable sources for the RHEL production distro, for 
Canonical Ubuntu (at least until profiteering supplants stakeholder 
business practices) the "versions" and "upgrades" mean installable 
executables ("binaries"), of course with source provided.  In part 
because unlike EL, derived from IBM RH (a strictly for-profit entity 
with public relations statements about community stakeholder issues 
other than financial parameters optimisation), LTS derives from Debian 
--  see

https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Debian-5FSocial-5FContract&d=DwICaQ&c=gRgGjJ3BkIsb5y6s49QqsA&r=gd8BzeSQcySVxr0gDWSEbN-P-pgDXkdyCtaMqdCgPPdW1cyL5RIpaIYrCn8C5x2A&m=YHVn3IEuYexuWWwLYQFegF7TqJbRDPX4ksA9J8RXARM&s=XSE0cgw_foccBTZVXJ7pOGgQIYLcGOA6wDU4YR10XNE&e= 

for further details.