Well, while I wouldn't give it one pipe, Jonny Lee Miller's focus on Lucy Liu and Rhys Ifans sleeping together is childish in a way that I don't think Holmes would act. It was more over the top than Robert Downey's jealousy of Jude Law's courting Kelly Reilly, although it was in the same ballpark. For me last season's "Déjà Vu All Over Again" was a low point that "The Marchioness" did not match. It is the type of episode that dislikers of the show can point to and say "See, they're not Holmes and Watson, just quirky TV detectives with the same name." It will be interesting to see how Benedict Cumberbatch reacts to Martin Freeman's upcoming marriage. I have a feeling it will be closer to "Elementary" than Cumberfans (and Johnlock shippers) will admit to, but we'll see.
The problem is that, as you and I, John, are Sherlockians, we look at "Elementary" through a different lens than a TV show fan with a casual knowledge of the Canon. The juvenile way that Downey and Miller react to their Watson's emotional involvements with someone outside the partnership is an expansion of the dismissive attitude evinced by Holmes in the Canon: "Miss Morstan has done me the honour to accept me as a husband in prospective." He [Holmes] gave a most dismal groan. "I feared as much," said he. "I really cannot congratulate you." And: "The good Watson had at that time deserted me for a wife, the only selfish action which I can recall in our association. I was alone." It is on these slender threads that the modern conceit of a Holmes jealous of the emotional infidelity of his only friend leaving him for another is founded. It's like the Holmes/Adler pairing so common among Sherlockians, pasticheurs and screenwriters. The respect Holmes felt for a worthy antagonist has been changed to love. The conventions of melodrama that the hero always gets the girl has been a Holmesian albatross since Gillette in 1899. With our 20th century Adler romance now comes the 21st century Holmes/Watson bromance.
Simple friendship is not enough these days. Watson's "Three Garridebs" wounding is now seen as something deeper than heterosexual male bonding: "Then my friend's wiry arms were round me and he was leading me to a chair. 'You're not hurt, Watson? For God's sake, say that you are not hurt!' It was worth a wound - it was worth many wounds - to know the depth of loyalty and love which lay behind that cold mask. The clear, hard eyes were dimmed for a moment, and the firm lips were shaking. For the one and only time I caught a glimpse of a great heart as well as of a great brain. All my years of humble but single-minded service culminated in that moment of revelation." Now we have Downey and Law sharing clothes like sorority sisters and secondary characters assuming Cumberbatch and Freeman are lovers. While gay undertones are written into the Warner Bros. series and the BBC, the fans are bring to the proceedings their own fevered imaginings, and mixing up the Canonical characters with those pale photons that share a name. You even have the Baker Street Babes talking about Canonical "hand porn" as evidence for something that Arthur Conan Doyle could never have written.
Miller's Holmes is aggressively heterosexual. Sex for him is a stimulant, leaving his brain "awash with neurochemicals". It had no emotional connection, except with Natalie Dormer's Irene Adler/Jamie Moriarty. "Is this all I am now? A piece of exercise equipment for your brain?" Unfortunately for Miller the answer was no. One of the things that "Elementary" did brilliantly was connect Miller's addiction to Irene Adler's death and then make Adler Moriarty. If the BBC could have gotten away with it, they would have done something similar with Cumberbatch and Andrew Scott. There is Scott's pick-up attempt of Cumberbatch in the beginning of "The Great Game" and his psychopathic "flirting" with Cumberbatch throughout both series. The sexual tension is so thick you can cut it with a knife. It is still a bridge too far to have a male Holmes and Moriarty romantically linked, even for British television.
Despite the opposite genders, "Elementary" executive producer Rob Doherty has declared that Holmes and Watson will not be romantically involved. Sherlockians who like the show could not be happier. TV show fans, however, are a fickle lot and Miller/Liu shipping is rampant. An episode like "The Marchioness" plays into that with Miller's peevish jealousy and sibling rivalry. It makes Miller less a Canonical Holmes, more an average TV character.
Miller's sexual escapades exist only for mental stimulation. While Miller has taken the Watson role of have an "experience of women which extends over many nations and three separate continents", it was Liu who came off as something of a prude. To have the viewer find out she slept with Ifans is jarring. It seems out of character, especially as the show never set up an emotional connection between the two. Sex makes everything complicated. Introducing it in a non-Canonical way will always leave a bad taste in a Sherlockian's mouth.