I'm not a lawyer, but as far as I understand it antitrust law/regulators don't really make the distinction of whether a company has a full-blown monopoly. What primarily matters is whether they either exercise monopoly power (e.g. raise prices or reduce product/service value without commensurate loss of sales to competitors) or engage in anticompetitive practices intended to drive competitors out of the market (predatory pricing/dumping, tying products across different markets, exclusivity agreements, refusing to sell to a company in one market because they're a competitor in another market).
In terms of pricing power for electronics I don't see it at this point. There are too many opportunities for shoppers to go elsewhere and everything gets arbitraged away via eBay extremely quickly.
That said, I also think that regulators should keep a close eye on what's going on in online retail, particularly when it comes to specific sections of the market like books/publishing.
