UPDATE: YES, from 01.03.2020 one does not need a degree to work as an IT specialist in Germany. Please see the following information (in German) for details:
Old answer left for the reference (the laws described below should still be valid, so that they are extended but not replaced with a new regulation) below:
One explanation I've come up with is that to apply for a Blue Card you do still need a degree, while to apply for a regular German work permit you don't need a degree
This is partly right. A degree is not necessarily needed. However, it still could be that you need to have a degree to apply for any of these 2 types of residence permits.
Historically, in Germany, there was a regular residence permit for workers that is issued according to §18 AufenthG. Then, after the EU introduced the Blue Card, a new paragraph was added to the immigration law: §19a AufenthG.
Also, §19 in general describes the residence permit for highly-qualified persons (who are expected to have higher education), while §18 describes the residence permit for all kinds of workers in general.
So, these paragraphs have different requirements and benefits (and I strongly advise you to dig into both of them). To get a Blue Card, a university degree is mandatory (please see details here, but it could indeed have been updated since 2013). Theoretically, according to §18a, to get a residence permit for workers, 3 years of working experience could be enough (even without a degree), if you were already in Germany before you apply for it. Another option to get a residence permit for workers without having a degree could be an agreement between Germany and another country, or individual permission (§ 18 Abs. 3 AufenthG).
If yo do not have any kind of degree after school, and if there is no special agreement between your country and Germany, it could be more complicated but maybe still possible for you to get a residence permit as a worker. This now slowly becomes too complicated for me to dig into German laws at this point, so please double check the following on your own:
If you apply for the regular residence permit for workers, in most cases, your application will be checked by a kind of job center (Bundesagentur für Arbeit), to check if you do not compete with Germans on the job market. For IT, there is a high demand for workers right now, so such a check should not be a problem, if you have a degree.
And if you do not have a degree, as far as I understand from § 18 Abs. 3 and §42 AufenthG, you can still get the permission after your qualifications are checked, but I'm not sure about it. Probably, for an IT position, you still have chances to get it, if you got a job offer already. The decision can depend on the salary or the specific requirements that a company has for a particular position, please see the document from the Arbeitsagentur, Section 2.2 for more details.
P.S. I'm not a lawyer.