You're conflating cash with assets. None of the companies you mentioned are trading at a discount to their cash balance.
Institutional investors don't value tech companies based on tangible book - they use P/E or EV / EBITDA multiples (or FCF multiples for software companies). The only companies that trade on net asset value (NAV) are financial companies such as banks. For those companies, the balance sheet structure is the opposite of traditional companies - assets such as cash represent liabilities (they're funds individuals have deposited in their account). As a result, the NAV framework is inappropriate to apply to tech companies.
Two specific points on the above examples:
(1) Cable companies are valued using a different investment framework. They are highly capital intensive businesses, where cash today does not reflect cyclical future capital expenditures. Furthermore, these businesses have a tremendous amount of leverage, and thus you have to look at net cash balances, not gross cash.
(2) Your Apple example is absolutely correct. This actually happened when Microsoft announced a special one-time dividend in 2004. This goes back to my 3rd point above - when companies hoard a significant cash balance without any plans for capital returns, investors start to discount the cash. This was Icahn's thesis when he went activist on Apple. However, I would caution against extrapolating this to companies that don't have significant cash balances.
I know it sounds tempting to say that cash doesn't generate great returns and is thus logically undervalued. There are two reasons why that's not the case.
(1) Investors usually use EV / EBITDA multiples to arrive at an enterprise value. EBITDA is prior to the recognition of interest expense / income - the earnings generation of cash does not matter here at all. After arriving at the EV, they then add cash and subtract debt (at a 1:1 value) to arrive at the equity value, and then divide by shares outstanding to arrive at the target price.
(2) Investors that use P/E multiples need to normalize for variations in cash balances by using ex-cash P/E multiples. For most companies, cash is a small percentage of the market cap such that P/E multiples are a close enough approximation to ex-cash P/E multiples. For companies with large cash balances, that's not the case, and the valuation method needs to be adjusted appropriately.
If your argument is that some investors fail to do this, you're absolutely right. However, they are doing so based on an error of judgement - not because they really believe cash shouldn't be valued on a 1:1 basis.