Considering the auto industry as a whole is somewhat misleading.
One must consider the message, the target and the specific marketer: In the big-ticket, "considered-purchase" sphere, there are distinct phases for the buyer. We can think of them as awareness, consideration and "shopping."
During the awareness phase, consumers are learning
about the available brands / products / features that could meet their needs or even learning that they have needs, based upon information presented in ads. These are messages from auto makers, dramatizing and romanticizing cars, with some detail about capabilities and features. Image and awareness are typical goals. Budgets are big and TV carries the burden. This awareness / image building phase can occur over years, leading consumers to establish general attitudes towards auto brands.
When consumers have an awareness of the brands, they begin to form a consideration set, focusing on the choices which will meet their needs. More detail regarding product capability and features is sought. Magazine and online ads can serve these messages, better targeted to the likely buyer of specific models, based on age, income, family size, interests, etc. These are also big budget, manufacturer, ads.
The consumer next reaches the shopping stage, where pricing and deals become key issues. At this point, local dealer ads and newspapers are more relevant. Yet, this decision is being made among brand choices stemming from the big budget advertsing that we discussed first.
Of course, none of these stages are pure, and messages overlap. Keep in mind that the decision / internet nexus you have identified goes well beyond the advertising
arena, and involves consumers' use of manufacturers' web sites or independent product comparison sites like Consumer's Reports, neither of which involve advertsing budgets.