Your initial statement is partially invalid and that's what's causing you some comparison difficulty. An associates degree is not generally the first two years of a bachelor's degree - but it can be.
The particular associates degree that represents that lower-level of the bachelor's degree is the Associate of Arts (AA) degree. It is usually intended as a non-vocational, academic degree specifically to facilitate transfer to a four-year (senior college) program with junior standing. It has little (if any) value in the workplace by itself.
An AA or AS with a specific vocational intent at the bachelor's degree level doesn't necessarily have any vocational value at the associates degree level. Engineering is a good example - an AS in Engineering intended to be used to transfer to a 4-year college does not qualify someone to become a lower-level engineer but instead it qualifies them to transfer to an upper level college/university. It might be useful vocationally for an engineering technician - then again, it might not. The intent is as a transfer credential and not as a vocational qualifier.
Other associates degrees tend toward the more vocational and qualify the holder for a specific job at a specific level. The Associate of Applied Science is an example as is the Associate of Science in Nursing. These do not transfer as directly into a bachelor's degree program as does an AA because of issues with content and level. Many students with an AAS or AS in [Subject] find that after two years in the community college, they still need almost 4 years to complete the bachelor's degree.
For the most part, the AS and AAS prepares technicians and technologists and not professionals and managers. The BA/BS (and graduate degrees) prepare the professionals and the managers.
In the field of education (such as adult ed, vocational, and workplace learning) a bachelor's degree is usually the lowest degree qualifying for licensing. BUT in a few fields within the vocations (plumbing, carpentry, auto mechanics) there is no bachelor's degree. Teachers of those vocations aren't usually required to have a bachelor's degree and some aren't required to have a degree at all but instead the trade license/certification in their field with some experience. It's partly for those people (teachers of trades and technical vocations) that an associates in adult/vocational ed would be designed.
There are also positions in industry for trainers who prepare workers to do their job. Many of these positions, when in a vocational field, also don't require a higher degree but instead certification and experience. Training of electricians or roofers, for example, doesn't require a master's degree. Very often, that associates degree is supplementing another in a technical field - such as Paramedic training or Law Enforcement - for people that conduct training in their area of expertise. Governments (at all levels) employ of lot of these folks with titles such as trainer, instructor, or (especially in public services) Training Officer.
Usually though - corporate level trainers as well as public school teachers need a bachelor's degree to be considered for a position and increasingly a master's to be competitive. In fact, about half of all public school teachers have a master's degree. Training and Development in the corporate/industrial world is a function of human resources and is very often contracted out to consultants.
Depending on your field of expertise, some of these jobs pay very well while others pay nothing (literally nothing - they're volunteers). Some are not the primary responsibility of the holder but instead an additional duty they perform - such as the Training Officer at a small fire department who is also primarily a fire fighter. Professional positions and advancement will require at least a bachelor's degree in almost all areas of specialty in all industries.
Take a look at these entries in the occupational outlook handbook for some more details about educational requirements, employment outlook, and earnings:
Training Specialists and Managers: http://www.bls.gov/oco/ocos021.htm
Teachers - Self Enrichment Education: http://www.bls.gov/oco/ocos064.htm
Teachers - Vocational: http://www.bls.gov/oco/ocos358.htm