I really do think there has been some confusion of distinction between Baroque and Rococco. I have to admit, my knowledge of Baroque ends at it being a musical period during the 17th to early 18th century.
In terms of costuming however, I would say that 18th century European (in particular French) fashion has to be classified as Rococco. The images posted above (Marie Antoinette, Madame de Pompadour most definitely are Rococco cosumes.
The 17th century had a wild mixture of styles, ranging from Jacobean to Puritans and of course styles diverged according to country. Baroque fashion probably originated from France where the style was championed by Louis XIV, the 'Sun King' (a trendsetter of his age). It was characterised by excessive ornamentation. For example it became fashionable to trim everything with bunches of ribbons. This can be seen in these men's 'petticoat' breeches:
Just some pics to illustrate Baroque style:
Illustration of Mlle. D'Hautefort
There is often confusion between Baroque and Rococco style because they both share those ornate and over-embellished characteristics. However, there is a marked difference in that Baroque fashion was weighted with a solidarity and heaviness whereas Rococco had a lightness, a fluidity. With the arrival of the Enlightenment, the 'freeing of the mind', this new found optimism was also reflected in fashion. Flowers, birds, and bows became dominant motifs in a style that highlighted a kind of idealized femininity. This was seen not just in costumes but also in all kinds of visual arts (broadly speaking, these eras we speak of apply to a multitude of things - interiors, architecture, music)
It was also during the Rococco period that the trendsetter also switched from France to England in the mid 18th century. There was a trend of neo-classicism that flourished amongst the English nobility that was highly thought of.
English Robes circa 1785
French gown circa 1780
The dress above demonstrates the trend of chinoiserie and detailed fabrics particular to the Rococco period.
Some more pics of typical Rococco costumes:
Madame Bergeret
I think a mix of both periods can be seen on the catwalk but I think it's really the structural features of the Baroque period that are being used. Especially in Balenciaga and Chanel's collections.
All pics from costume.org