It's about lacking of decent fonts.
When I saw this statement the first time, I ignored it. Now you caused me to waste my time to prove how wrong this statement is. I just scanned all available font collections on my Mac, with support for character "ę". Here you go:
UNICODE Name: LATIN SMALL LETTER E WITH OGONEK
Collection: ModernFutura: Condensed Medium, Medium, Condensed Bold, Medium Italic
Gill Sans: Light, Regular, Bold, Italic, Light Italic, Bold Italic
Helvetica Neue: Condensed Black, Condensed Bold, Light, Medium, Regular, Ultralight, Bold, Italic, Ultralight Italic, Bold Italic
Collection: PDFCourier: Regular, Bold, Bold Oblique
Helvetica: Regular, Bold, Oblique, Bold Oblique
Times: Regular, Bold, Italic, Bold Italic
Collection: TraditionalCochin: Regular
Didot: Regular
Collection: WebAndale: Mono
Arial: Bold, Bold Italic, Regular, Black regular
Comic Sans MS: Regular , Bold
Georgia: Bold, Bold Italic, Italic, Regular
Impact: Regular
Times New Roman: Bold, Italic, Bold Italic, Regular
Trebuchet MS: Bold, Bold Italic, Italic, Regular
Verdana: Bold, Bold Italic, Italic, Regular
Collection: FunAmerican Typewriter Condensed: Regular, Light, Bold
American Typewriter: Light, Regular, Bold
Herculanum: Regular
Marker Felt: Thin, Wide
Zapfino: Regular
Collection: Fixed Width - for us, programmers
Andale Mono
Courier: Regular, Bold, Oblique, Bold Oblique
Courier New: Bold, Bold Italic, Italic, Regular
Menio: Bold Bold Italic, Italic, Regular
Monaco: Regular
Would you call it decent enough?