I think they mean that they are so slow in improving their products that you can think of them like "eternal", because you'll not feel the need to change them (within the same brand), considering that there will be no big improvements in their products for... 10 years? More? As an example, consider the ES8: it was from 2015. Its successor, the ES920, is from 2020. IMHO the latter is just the old ES8 with a very few more customization options in the piano engine, a lighter (but very plasticky and less refined) case, and better speakers. So, after 5 years just very small, almost cosmetic, improvements of one of their best selling products. In other words, we could say they think their products should not get "big" improvements for at last 10 years.