Ask HN: How viable are linux alternatives to PS and Illustrator (Gimp, Inkscape)

I am beginner programmer and web designer. I use ubuntu for everything. However, I've heard and read time and time again that Inkscape and Gimp are good, but just not as good as PS and Illustrator, and that you 'can not become serious web designer' unless using PS and Illustrator. How true is this? Is the difference noticable only in high-end features or right from the beginning?