There's no well-defined line of what software is expressive (and eligible for copyright) and what software is merely functional. I would argue that this software is merely functional -- there's not all that much code, and there are only a few ways you can write code that performs the same function. It's largely mechanical.
On the other hand, the Nintendo logo is actually contained in the ROM, as part of the protection mechanism. This was probably done as a "copyright/trademark trick" -- the logo is certainly expressive (and eligible for copyright), so in order to make a clone cartridge, you would have to copy this logo.
Unfortunately for Nintendo, Sega
tried this trick in court and lost a couple of years later. That court case actually established the precedent I'm alluding to above... a few choice quotes from
the decision:
In some circumstances, even the exact set of commands used by the programmer is deemed functional rather than creative for purposes of copyright. "[W]hen specific instructions, even though previously copyrighted, are the only and essential means of accomplishing a given task, their later use by another will not amount to infringement."
[...]
Sega's trademark security system (TMSS) initialization code not only enables video game programs to operate on the Genesis III console, but also prompts a screen display of the SEGA trademark and message. As a result, Accolade's inclusion of the TMSS initialization code in its video game programs has an effect ultimately beneficial neither to Sega nor to Accolade. A Genesis III owner who purchases a video game made by Accolade sees Sega's trademark associated with Accolade's product each time he inserts the game cartridge into the console. Sega claims that Accolade's inclusion of the TMSS initialization code in its games constitutes trademark infringement and false designation of origin in violation of [...] the Lanham Trademark Act. Accolade counterclaims that Sega's use of the TMSS to prompt a screen display of its trademark constitutes false designation of origin under Lanham Act section 43(a), 15 U.S.C. Section 1125(a).
Because the TMSS has the effect of regulating access to the Genesis III console, and because there is no indication in the record of any public or industry awareness of any feasible alternate method of gaining access to the Genesis III, we hold that Sega is primarily responsible for any resultant confusion. Thus, it has not demonstrated a likelihood of success on the merits of its Lanham Act claims.
This legal issue was later revisited in a slightly different form (with mixed results) in Lexmark V. Static Control Components -- however, in that case, there was a lot more code involved than the boot ROM we're talking about here, so much more room for claims of expressive code.
