Skalp materials are optimized to be printed. Layout rasterize everything to 300 dpi (high) or 150dpi (medium) depending on the Document Setup > Paper > Rendering Resolution > Output quality setting.Even if you use vector the lines will be rasterized by you printer driver before it’s send to the printer. Only a pen plotter plots real vector information.
Skalp materials are made at 300dpi considering the chosen scale. This means if you use a skalp material on the correct scale you get the best result your printer can print. If you zoom in on your screen this texture look jagged and blurry.
The difference between SketchUp and layout is pure a difference in rendering engine between the two programs. If you change Document Setup > Paper > Rendering Resolution > Edit quality setting to high you improve the quality on your screen to 150dpi, but it really slow down your computer! Keep in mind if you set ‘Edit quality’ to high you get 150 dpi, if you set ‘Output quality’ to high you get 300dpi. It is not really WYSIWYG.