With Klimt, I think it was a matter of familiarity with his subject matter. Klimt was notorious for the women in his life, and he used his mistresses as subjects for his art. Nothing new in that, except that it is amazing that in turn of the century Vienna he managed to have women of such high social status pose willingly for him for such erotic works. For instance: his first version of "Judith Holding The Head Of Holofernes". Viennese socialite--and Klimt mistress--Adele Bloch Bauer posed for the painting, half naked, and with an unrestrained, undeniable look of sexual ecstasy on her face. It can hardly be imagined that a paid model, without such an intimate relationship with the artist, could have equalled such force as a subject.
Beardsley, in contrast, never had a fulfilling sex life, so his work is less true to life and more accurately described as grotesque(In the original sense of the word) or satirical. Schiele was under intense scrutiny by the law and had to be circumspect after run-ins with them. The fact that he managed such powerful work under such scrutiny is a testament to his talent.
With Klimt, a happy medium was achieved; he had intimate, erotic subjects to paint and the vast talent to do so well. I don't think it is restraint that gives his work such power, but familiarity. When he paints subjects without models, a distinct drop in tension is evident. Take his several works that combined water and lesbian themes(Klimt, like most men, was fascinated with lesbians, but did not mange to get two women to strike a sapphic pose for him). They just aren't as powerful as the paintings that featured his mistresses.
By the way, Klimt always paid tribute to Beardsley, particularly in his Beethoven frieze.
