Maybe not - but we could blame them for failure to comply with the regulations :
The Road Vehicles (Construction and Use) Regulations 1986
63.—(1) Save as provided in paragraph (4), this regulation applies to—
(b)heavy motor cars, motor cars and motor cycles, not being agricultural motor vehicles or pedestrian-controlled vehicles;
(c)agricultural motor vehicles driven at more than 20 mph; and
(2) Subject to paragraphs (3) and (5), every vehicle to which this regulation applies shall be equipped with wings or other similar fittings to catch, so far as practicable, mud or water thrown up by the rotation of its wheels or tracks.
Can't see how some of the motorcycles on the market comply with this requirement. And "Paragraph 4 exemptions" do not include any motorcycle related cases.