Not really. I took a look at kind of a cable Sennheiser bundles with each headphone from the website:
HD 559: 6.3 mm plug.
HD 560 S: 6.3 mm plug.
HD 569: 6.3 mm plug + 3.5 mm plug.
HD 579: 6.3 mm plug.
HD 599: 6.3 mm plug + 3.5 mm plug.
HD 600: 6.3 mm plug.
HD 650: 6.3 mm plug.
HD 660 S: 6.3 mm plug + 4.4 mm balanced.
HD 800 S: 6.3 mm plug + 4.4 mm balanced.
HD 820: 6.3 mm plug.
So really the 3.5 mm cables are an exception that are also bundled with Sennheiser's audiophile-tier headphones and absolutely everything has a 6.3 mm plug out of the box.
That 6.3mm / 1/4" plug is 3.5mm + converter (you just pull it apart comes apart into two pieces), at least on 5xx and 6xx range. It's not even screwed on, just a tight friction fit. Unless, that is, Sennheiser decided to cheapen out in the last 10 years and redesigned them...
Never had original 8xx cables to check but I would be surprised if they weren't the same.
Which means that they have indeed cheapened out with a recent refresh - which is a shame. I have the cable I describe on the headphones I am quite literally wearing on my head at this very moment (HD 600) and identical ones were present in 59x and 650 from the era. Glad to know, TIL.
Edit: the 3.5mm male to headphone is Sennheiser 81435 [0] the 6.3mm male to 3.5mm female that fits over it is Sennheiser 562507 [1].
I bought the HD600 last year and it came with the 6.3mm to 3.5mm removable adaptor. This was in Europe maybe the cabling is different, or there are multiple packagings for different use cases (likely). The cables are removable so its easy for them to have different SKUs.
